Introduction: Why Understanding Testosterone Therapy Matters

Testosterone is a hormone that plays a major role in a man’s body. It affects energy levels, muscle mass, bone strength, mood, and sexual health. As men get older, their testosterone levels often begin to drop. This natural decline can lead to fatigue, low sex drive, depression, weight gain, and other changes. Because of this, many men are turning to testosterone therapy to feel better and improve their quality of life.

Testosterone therapy is a medical treatment that raises the level of testosterone in the body. It is usually given through injections, skin gels, patches, or implants. While it is helpful for some men—especially those with a condition called hypogonadism—it is not always safe for long-term use in every case. Many men use it for more energy, better mood, or improved physical performance, even if they do not have a medical need. Some get it from clinics or online sources without a full check-up. Others begin therapy without understanding the long-term effects it can have on their bodies.

In recent years, testosterone therapy has become more common. Ads often promote it as a solution for aging or to help men feel younger. However, doctors and scientists are still studying what happens when testosterone is used over long periods of time. Some studies show benefits, but others show risks. These risks can affect the heart, liver, blood, mood, sleep, and even fertility. Because of this, medical experts are calling for more awareness and better guidelines for its use.

Most of the research on testosterone therapy focuses on short-term effects. People often feel more energetic and stronger in the first few months. They may notice better sexual performance, better sleep, and less anxiety. But fewer studies have tracked men who have used testosterone for many years. Some of the long-term effects only appear after months or even years of treatment. This makes it important for men to ask questions and get the facts before starting or continuing therapy.

There are several important things to understand about long-term testosterone use. First, it can affect the heart and blood vessels. Some studies have shown that it may raise the risk of heart attacks or strokes, especially in older men or those with existing heart problems. It may also change cholesterol levels and increase red blood cell counts, which can make the blood thicker. This raises the chance of blood clots forming.

Testosterone therapy can also affect the prostate. It may cause the prostate to grow larger, leading to urination problems. In some cases, doctors worry that it may increase the risk of prostate cancer, though this is still debated. In addition, therapy can reduce the body’s natural ability to make its own testosterone. This may lead to testicular shrinkage or even infertility in some men.

Mood and brain function are also areas of concern. While testosterone can help with depression and tiredness at first, long-term use may cause mood swings, irritability, or even aggression in some men. There are also questions about whether it affects memory or thinking skills as men age.

Sleep problems are another risk. Some men on testosterone develop or worsen sleep apnea, a condition where breathing stops and starts during sleep. Others report poor sleep quality or feeling restless at night.

Because of all these possible effects, medical experts say it is important to follow clear rules when using testosterone therapy. A full exam, lab tests, and regular follow-ups are needed. These steps help doctors check for side effects and decide if the treatment is still safe and needed.

Testosterone therapy can help men who truly need it, but it is not a magic solution for aging or fatigue. Long-term use must be guided by science and medical care. Understanding the real risks and benefits helps men make better choices about their health. More men are asking questions about testosterone therapy, especially about what happens years after starting it. Answering those questions with facts is key to staying safe and well-informed.

What Is Testosterone Therapy and Who Typically Needs It?

Testosterone therapy is a treatment that helps raise the levels of testosterone in the body. Testosterone is a hormone made mainly in the testicles. It plays a key role in male health, including muscle growth, bone strength, energy, mood, sex drive, and sperm production. When the body does not make enough testosterone, doctors may prescribe testosterone therapy to help bring hormone levels back to normal.

There are several forms of testosterone therapy. The most common types include injections, skin gels, skin patches, and pellets placed under the skin. Each method has its pros and cons, and doctors choose the best one based on a person’s health, age, lifestyle, and treatment goals.

When the Body Lacks Testosterone

Low testosterone is called hypogonadism. It can happen for many reasons. Sometimes the testicles are not working as they should. This may happen due to injury, infection, chemotherapy, or certain medical conditions. In other cases, the brain may not send the right signals to the testicles to make testosterone. This type is often due to problems in the hypothalamus or pituitary gland. Both types can cause the same symptoms: fatigue, low sex drive, muscle loss, mood changes, and problems with focus or memory.

Some men are born with conditions like Klinefelter syndrome that cause lifelong low testosterone. Others develop it later in life due to aging, obesity, diabetes, or other chronic health issues. Doctors perform blood tests to check testosterone levels. These tests are usually done in the morning, when hormone levels are highest. A diagnosis of hypogonadism is made when blood levels are low on at least two separate tests and the person has symptoms of low testosterone.

Who Needs Testosterone Therapy?

Testosterone therapy is approved for men who have been diagnosed with hypogonadism due to known medical causes. This includes men with damage to their testicles, diseases that affect hormone production, or genetic disorders. These individuals often show clear signs of low testosterone, and their bodies cannot make enough of the hormone on their own. For them, testosterone therapy can help improve mood, energy, muscle strength, and sexual function.

Testosterone therapy is not meant for men who simply have low energy or a lower sex drive with age. Some people may ask for testosterone to feel younger or more active, but if their testosterone levels are still in the normal range, therapy may not be safe or helpful. Using testosterone without a true medical need can raise the risk of side effects and health problems.

Off-Label Use and Anti-Aging Clinics

In recent years, more men have been given testosterone therapy without clear medical reasons. Some clinics market testosterone as a way to slow aging, build muscle, or increase sexual performance, even when hormone levels are normal. These uses are called “off-label” because they are not approved by health authorities like the FDA.

While some men feel better for a while, the risks of long-term use without true need are not fully understood. Taking testosterone when it is not medically needed can harm the body’s natural hormone balance. It may also raise the risk of heart problems, sleep issues, and fertility loss.

Proper Diagnosis Is Important

Before starting therapy, doctors need to check for signs of low testosterone and confirm the diagnosis with lab tests. Symptoms like low energy or reduced sex drive can also be caused by other health issues such as depression, thyroid problems, poor sleep, or medication side effects. A thorough evaluation helps make sure that testosterone is the right treatment.

Doctors may also look for other causes of low testosterone that can be treated in different ways. For example, weight loss, better sleep, and managing stress may improve hormone levels naturally in some men. In these cases, lifestyle changes may be tried before hormone therapy is started.

Testosterone therapy can help certain men when used for the right reasons and under medical care. It is not meant as a cure-all for aging. Understanding who really needs therapy helps reduce health risks and ensures that treatment provides real benefit.

How Does Testosterone Therapy Work in the Body Over Time?

Testosterone is a hormone made mostly in the testicles. It helps control many important body functions in men. These include building muscle, keeping bones strong, producing red blood cells, supporting sex drive, and helping with mood and energy. As men get older, testosterone levels slowly drop. Some men develop low levels earlier due to health problems. Testosterone therapy (TT) is used to bring hormone levels back to normal.

When testosterone is given as a treatment, it affects the body in many ways. Some effects show up quickly. Others take time and may become clearer after months or even years. Understanding these effects helps show how TT works in the long term.

Muscle Mass and Strength

One of the most common reasons men start TT is to improve muscle size and strength. Testosterone increases the growth of muscle fibers. It also helps the body make protein more efficiently. This is why many men notice more muscle tone and better performance during workouts. Most changes in muscle mass happen in the first 3 to 6 months. With continued use, strength may continue to improve for up to 1 year.

Over the long term, testosterone keeps helping maintain muscle mass, especially in older men. This can improve mobility and reduce the risk of falls. However, if testosterone levels become too high, it may lead to muscle tightness or swelling.

Fat Distribution

Testosterone also plays a role in how the body stores fat. Men with low testosterone often have more body fat, especially around the belly. They may also have a condition called metabolic syndrome, which raises the risk for heart disease and diabetes.

Testosterone therapy can reduce fat mass, especially visceral fat (fat around the organs). Over time, this can lead to a leaner body shape. Most changes in fat levels start to show in the first few months. With ongoing treatment, fat levels may stay lower, especially if combined with regular exercise and a healthy diet.

Red Blood Cell Production

Testosterone helps the bone marrow make red blood cells. These cells carry oxygen to the muscles and organs. When testosterone levels go up, red blood cell counts often increase. This can lead to better energy and stamina. Many men on TT say they feel less tired, especially after several months of treatment.

However, too many red blood cells can be harmful. The blood may become thicker and raise the risk of clots, stroke, or heart attack. Doctors usually check red blood cell levels (hematocrit) during therapy. If the number gets too high, the dose may need to be lowered or paused.

Sex Drive and Sexual Function

Another effect of testosterone is on sexual health. Testosterone is key to a healthy libido (sex drive). Men with low testosterone often lose interest in sex. They may also have trouble getting or keeping an erection.

After starting TT, many men notice improved sex drive within weeks. Erections may become stronger and more regular over time. These effects often continue with long-term use. In older men or those with other health problems, the benefits may be slower or less noticeable.

Mood and Energy

Low testosterone is often linked with mood changes. Men may feel depressed, anxious, or tired. They might also find it hard to focus or feel motivated.

Testosterone therapy can help improve mood and boost energy levels. Some men feel better within a few weeks. Others notice gradual changes over several months. The effects tend to be stronger in men who had very low levels to begin with.

Mood benefits may level off over time. Regular checkups and mental health support can help maintain well-being.

Cognitive Function

Some research suggests that testosterone may play a role in memory and thinking skills. It may help protect brain cells and support clearer thinking. In long-term use, some men report better focus and fewer memory problems. However, studies on this are still ongoing, and the results are mixed.

Timeline of Changes

Different parts of the body respond to testosterone at different speeds. For example:

Libido often improves within 3 to 6 weeks
Mood and energy changes may start within a month
Muscle mass and strength grow steadily over 3 to 12 months
Fat loss usually takes a few months
Red blood cell levels may rise after several weeks
Bone strength and density changes take 6 to 12 months or more

These changes depend on age, health, lifestyle, and how low the testosterone level was at the start. Regular monitoring helps make sure the body is responding safely and effectively over time.

Testosterone therapy has clear effects on many systems in the body. Some benefits appear quickly, but many build up slowly. Over time, these changes shape a man’s strength, energy, sexual health, and well-being. However, careful use and regular doctor visits are key to avoiding risks and keeping treatment on track.

What Are the Cardiovascular Risks of Long-Term Testosterone Therapy?

Testosterone therapy has been shown to increase energy, boost muscle mass, and improve sexual health in men with low testosterone levels. However, long-term use of testosterone may also carry some risks for heart health. Understanding how testosterone therapy can affect the cardiovascular system helps patients and doctors make safer treatment choices.

Blood Pressure and Heart Function

Testosterone therapy can raise blood pressure in some men. This happens because testosterone may cause the body to hold onto more water and salt. When this happens, the volume of blood increases, which puts more pressure on the blood vessels. Over time, higher blood pressure can strain the heart and increase the risk of heart attacks, strokes, and heart failure.

Some studies show that testosterone therapy may increase heart rate and the strength of heart contractions. In healthy men, these changes might not cause problems. But in men who already have high blood pressure or heart disease, even small increases in blood pressure or heart activity may be dangerous.

Blood Clot Risk and Erythrocytosis

Testosterone therapy increases red blood cell production. While this may improve energy and stamina, it can also lead to a condition called erythrocytosis. Erythrocytosis means there are too many red blood cells in the blood. This thickens the blood and makes it harder for the heart to pump.

Thicker blood increases the risk of blood clots forming in the veins or arteries. Blood clots can lead to serious problems like deep vein thrombosis (DVT), pulmonary embolism (PE), heart attacks, or strokes. Some men using testosterone therapy have been found to have hematocrit levels (a measure of how much of the blood is made up of red blood cells) above safe limits. Doctors usually monitor hematocrit regularly in patients on testosterone to reduce these risks.

Arterial Plaque and Atherosclerosis

There is some concern that long-term testosterone therapy may speed up the buildup of plaque in the arteries. Plaque is made of fat, cholesterol, and other substances. When plaque builds up in the arteries, the condition is called atherosclerosis. This narrows the blood vessels and reduces blood flow to the heart, brain, and other parts of the body.

A study from 2015 using coronary CT scans showed that men who received testosterone therapy had a greater increase in non-calcified plaque in their arteries over one year compared to men who did not receive treatment. Non-calcified plaque is softer and more likely to break loose, which can cause a heart attack or stroke. However, more long-term studies are needed to fully understand whether testosterone therapy truly causes or worsens atherosclerosis in most patients.

Lipid Profile and Cholesterol Levels

Testosterone can affect cholesterol levels in the blood. It may lower HDL (high-density lipoprotein), also known as "good cholesterol," which helps remove bad cholesterol from the arteries. At the same time, testosterone therapy may not significantly reduce LDL (low-density lipoprotein), or "bad cholesterol," in most men.

Lower levels of HDL cholesterol can make heart disease more likely, especially in men who already have risk factors such as obesity, diabetes, or smoking habits. Some studies report mixed results, with changes in cholesterol levels depending on the dose and type of testosterone used.

Inflammation and Cardiovascular Markers

Inflammation in the body is linked to a higher risk of heart disease. Some research has shown that testosterone may reduce certain markers of inflammation, such as C-reactive protein (CRP), in men with low testosterone. However, other studies have shown increases in inflammatory markers or no change at all.

Because of these mixed results, it's unclear whether testosterone therapy helps or harms long-term inflammation in the blood vessels. Differences in patient health, age, and treatment type may explain why results vary from study to study.

The FDA Black Box Warning and Ongoing Research

In 2015, the U.S. Food and Drug Administration (FDA) added a black box warning to testosterone products. This is the most serious warning the FDA can issue. It tells patients and doctors that testosterone therapy may increase the risk of heart attack and stroke, especially in older men and those with existing heart problems.

The FDA also required drug makers to conduct more studies to better understand these risks. One major trial, called the TRAVERSE study, was designed to look at the long-term effects of testosterone on heart health. Early results suggest that risks may vary depending on age, health status, and how low a man’s natural testosterone levels are before treatment.

While testosterone therapy can offer benefits to men with low testosterone, the potential effects on the heart and blood vessels must be taken seriously. Risks include higher blood pressure, increased red blood cell count, more plaque in the arteries, changes in cholesterol levels, and possibly more blood clots. All men considering testosterone therapy should have their heart health checked before starting treatment and continue regular follow-up testing during use.

Does Testosterone Therapy Affect Fertility and Testicular Size?

Testosterone therapy (TT) is commonly used to treat men with low testosterone levels. While this treatment can help improve energy, muscle mass, and mood, it also has important effects on fertility and the size of the testicles. These effects happen because of how testosterone interacts with the body’s natural hormone system.

How Testosterone Affects the Body’s Hormone System

The body makes testosterone through a process controlled by the brain. The hypothalamus and the pituitary gland work together to send signals to the testes. These signals come in the form of two hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH tells the testes to make testosterone, and FSH helps with sperm production.

When a man takes testosterone from outside the body—such as by injection, gel, or patch—the brain senses that there is already enough testosterone. As a result, the hypothalamus reduces the signals it sends. This causes the pituitary gland to make less LH and FSH. Without enough of these hormones, the testes stop making sperm and slow down their own testosterone production.

This is called a negative feedback loop. It is the body’s natural way of keeping hormone levels balanced. However, in the case of testosterone therapy, this system gets turned off for as long as the therapy continues.

Sperm Production Suppression and Infertility

Because the testes need LH and FSH to make sperm, a drop in these hormones leads to a drop in sperm production. In many cases, men on long-term testosterone therapy may produce little or no sperm. This condition is called azoospermia.

This change can make it hard or impossible to father children. In some men, even short-term use of testosterone therapy can cause sperm counts to fall. The risk increases with longer use and higher doses.

Infertility due to testosterone therapy is usually not permanent, but recovery can take time. Once the therapy stops, the brain needs to start sending signals again. It may take several months or even over a year for sperm production to return to normal levels. In some cases, especially after long-term therapy, full recovery may not happen.

Men who wish to have children in the future should speak with a doctor before starting testosterone therapy. Other treatments, such as clomiphene citrate or human chorionic gonadotropin (hCG), may help boost testosterone levels while protecting sperm production.

Testicular Atrophy: Shrinking of the Testicles

Another noticeable effect of testosterone therapy is shrinking of the testicles, known as testicular atrophy. This happens for the same reason sperm production stops—low levels of LH and FSH. Without these hormones, the cells in the testes do less work and begin to shrink in size.

Testicular atrophy can begin within a few months of starting therapy. The shrinkage may be mild or more noticeable, depending on the dose and duration of treatment. While not usually painful, it may cause concern for men who notice changes in the appearance of their genitals.

This change is also often reversible, but recovery takes time. After stopping testosterone therapy, the testes may return to their normal size once the brain begins sending hormone signals again. However, in some men, the size does not fully return to what it was before therapy.

What to Expect After Stopping Therapy

After stopping testosterone therapy, the body slowly restarts its own hormone system. Sperm production and testicular size may begin to improve, but this process can be slow. Some men experience low energy, mood changes, or reduced sexual function during this time because of the sudden drop in testosterone.

Doctors may use medications to help restart the natural hormone process. These medicines can help the pituitary gland make more LH and FSH, which supports the testes in making sperm and testosterone again. This approach is sometimes called hormone restoration or recovery therapy.

Testosterone therapy can greatly affect a man’s fertility and testicular size. The treatment lowers the body’s natural hormone signals, which leads to reduced sperm production and smaller testicles. These changes can lead to temporary or sometimes long-lasting infertility. Recovery is possible, especially if testosterone therapy is stopped early. Men who are planning to have children should carefully weigh these risks and discuss options with a healthcare provider before beginning therapy.

Effects on Prostate Health and Cancer Risk

Testosterone therapy (TT) can affect the prostate, a small gland located just below the bladder in men. The prostate helps make semen, the fluid that carries sperm. Since testosterone plays a role in the growth and function of the prostate, it is important to understand how long-term testosterone therapy may impact prostate health.

Testosterone and Prostate Size (BPH Risk)

As men age, their prostates often get larger. This condition is called benign prostatic hyperplasia (BPH). It is not cancer, but it can cause uncomfortable symptoms. These include trouble starting urination, weak urine flow, and the need to urinate often, especially at night.

Testosterone can make the prostate grow. Because of this, some men on long-term testosterone therapy may notice an increase in urinary symptoms linked to BPH. Studies show that TT may slightly increase prostate volume over time, especially in older men. However, the changes are usually small. In many cases, the increase in size does not cause major problems. Still, men who already have BPH or urinary symptoms before starting TT may see their symptoms worsen.

Doctors usually monitor for signs of BPH during treatment. If symptoms become too bothersome, testosterone doses may be adjusted, or treatment may be stopped. Sometimes, medications that relax the muscles of the prostate are used alongside TT to reduce urinary issues.

Testosterone and PSA Levels

Prostate-specific antigen (PSA) is a protein made by the prostate. PSA levels are measured with a blood test and can be used to screen for prostate problems, including cancer. PSA levels can rise for many reasons—not just cancer. Infections, inflammation, or even a recent prostate exam can raise PSA temporarily.

Testosterone therapy may cause PSA levels to increase. This is because testosterone stimulates prostate tissue, which may lead to more PSA being made. Research shows that in most men, PSA levels rise slightly after starting TT, especially in the first 6–12 months. However, the increase is usually within the normal range.

A small number of men may have a larger jump in PSA levels. If that happens, more tests such as a repeat PSA, urine tests, or a prostate biopsy may be needed to rule out cancer. Because of this, doctors often check PSA levels before starting TT and then monitor regularly, usually every 6 to 12 months.

Does Testosterone Therapy Cause Prostate Cancer?

One of the biggest concerns with testosterone therapy is whether it increases the risk of prostate cancer. For many years, it was believed that higher testosterone levels could “feed” prostate cancer, making it grow faster. This belief came from older studies showing that removing testosterone (called androgen deprivation therapy) could slow down prostate cancer in advanced cases.

However, more recent research has challenged this idea. Several large studies and reviews have found no strong link between testosterone therapy and a higher risk of developing prostate cancer. In fact, men with low testosterone levels may already have a higher risk of more aggressive prostate cancers.

Some researchers believe that once testosterone levels reach a certain point, higher levels may not further increase cancer risk. This idea is called the saturation model. According to this theory, the prostate becomes "saturated" with testosterone, and extra hormone beyond that level does not make the tissue grow more.

Even though TT may not directly cause prostate cancer, it can still make hidden cancer grow faster. That is why doctors are cautious. TT is not recommended for men who have current prostate cancer or a history of it unless they are under close monitoring by a cancer specialist.

Monitoring and Safety Guidelines

Before starting testosterone therapy, most healthcare providers will:

Check PSA levels
Perform a digital rectal exam (DRE)
Ask about urinary symptoms and family history of prostate cancer

After starting treatment, men usually have their PSA levels checked again at 3 to 6 months, and then at least once a year. If PSA rises more than expected or if urinary symptoms worsen, doctors may pause treatment or order further tests.

Testosterone therapy may slightly enlarge the prostate and raise PSA levels. It may also make pre-existing urinary problems worse. However, current research does not show that testosterone therapy increases the risk of getting prostate cancer in healthy men. Regular monitoring of PSA and prostate health helps reduce risk and catch any issues early. Long-term safety is best ensured by working closely with a healthcare provider.

How Does Long-Term Use Influence Mood, Mental Health, and Cognitive Function?

Testosterone is a hormone that affects more than just the body. It also plays a role in how the brain works and how a person feels emotionally. Many men begin testosterone therapy to feel more energetic or to improve their mood. Some even report feeling more confident or motivated in the short term. But when testosterone therapy is used for a long time, it may have both helpful and harmful effects on mental health and brain function.

Mood Improvement and Depression

Low testosterone levels have been linked to symptoms of depression, sadness, and low energy. Some studies show that men with low testosterone may feel better emotionally after starting testosterone therapy. In certain clinical trials, men who had both low testosterone and mild to moderate depression showed improvement in their mood after taking testosterone for several months.

However, testosterone therapy does not work the same way for everyone. The benefits on mood seem to be more likely in men who have both low testosterone and depression. Men with normal levels of testosterone or those with other causes of mood disorders may not get the same results. For these reasons, testosterone is not considered a first-choice treatment for depression. It may help some people, but it should be used carefully and only after discussing mental health history with a doctor.

Anxiety and Emotional Stability

Some men also report less anxiety and greater emotional control after starting testosterone therapy. This could be because testosterone has effects on brain chemicals such as serotonin and dopamine, which help regulate mood and emotion. Studies have found that testosterone may reduce feelings of nervousness or fear in men who had low hormone levels to begin with.

At the same time, it is important to understand that emotional balance does not always improve with long-term testosterone use. Some men may experience changes in emotional reactions that become stronger or harder to control. In some cases, testosterone can lead to mood swings or sudden changes in feelings, especially when doses are too high or levels in the blood rise too quickly.

Aggression and Irritability Risks

One possible risk of long-term testosterone therapy is an increase in irritability or aggressive behavior. This does not happen to most men, but it is a known effect that has been seen in some clinical settings and research studies. This side effect is more common when testosterone levels become too high, either from using more than prescribed or from unmonitored hormone therapy.

In some men, high testosterone levels can cause quick mood changes, bursts of anger, or aggressive thinking. This is sometimes called “roid rage,” a term more often linked to steroid abuse in athletes or bodybuilders. While testosterone therapy is safer and more controlled than illegal steroid use, it still carries this risk if not monitored closely. Doctors usually prevent this by adjusting the dosage and checking blood levels regularly.

Effects on Thinking and Memory

There is also growing interest in how testosterone therapy affects brain function over time. Testosterone has receptors in the brain and may support mental sharpness and memory. Some research suggests that testosterone therapy may improve certain types of thinking, especially in older men who have low hormone levels. These include attention, problem-solving, and memory recall.

However, other studies have shown no major changes in thinking ability with testosterone use. The results are mixed. Some clinical trials suggest that testosterone may help with short-term thinking tasks, while others show no improvement or only small effects. More long-term research is needed to understand if testosterone therapy can truly protect the brain from aging-related problems like dementia or Alzheimer’s disease.

Long-Term Safety and Monitoring

Because testosterone affects the brain and emotions, regular checkups are important during therapy. If a man begins to feel more anxious, depressed, or angry after starting testosterone, this should be reported to a healthcare provider. Emotional and mental changes can be signs that hormone levels are too high or that the body is reacting poorly to the treatment.

Doctors may adjust the dose, change the form of testosterone being used, or recommend working with a mental health professional if needed. Balancing the hormone levels carefully can help reduce emotional side effects and improve overall well-being.

Testosterone therapy can influence mood, mental health, and thinking ability. It may help reduce depression and anxiety in men with low hormone levels, but it can also cause emotional changes like irritability or aggression if not managed properly. The long-term effects on memory and brain health are still being studied, and more evidence is needed. Regular monitoring and honest communication with healthcare providers are key to staying safe and mentally healthy during testosterone therapy.

What Happens to Natural Testosterone Production During and After Therapy?

Testosterone therapy can be helpful for men with low testosterone. However, it can also affect the body’s ability to make its own testosterone. Understanding how this happens is important for anyone considering long-term treatment. This section explains what occurs inside the body during testosterone therapy and what might happen if the therapy is stopped.

How the Body Normally Makes Testosterone

In healthy men, the body makes testosterone through a system called the hypothalamic-pituitary-gonadal (HPG) axis. This system works like a chain:

The hypothalamus (a part of the brain) sends a signal to the pituitary gland.
The pituitary gland releases two hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
These two hormones travel to the testicles.
The testicles then produce testosterone and sperm.

This process is like a feedback loop. When testosterone levels drop, the brain sends more signals to make more. When testosterone levels are high, the brain sends fewer signals.

How Testosterone Therapy Changes This System

When a man starts using testosterone therapy, the body sees the hormone as “enough” or even “too much.” As a result, the brain slows down or stops sending signals to the pituitary gland. This causes a drop in LH and FSH levels.

Without LH and FSH, the testicles do not get the signal to make testosterone. This is known as suppression of natural testosterone production. Over time, the body becomes dependent on the outside (exogenous) testosterone instead of making its own.

This suppression can begin within a few weeks of starting therapy. The longer therapy continues, the more the natural system slows down. In some men, it may shut down almost completely.

Testicular Shrinking and Sperm Production

A common result of this suppression is testicular atrophy, or shrinking of the testicles. The testicles become smaller because they are not doing their usual job of making testosterone and sperm. This change does not usually cause pain, but it can be noticeable.

Sperm production also drops. Many men on testosterone therapy have very low sperm counts. Some may become infertile while on therapy. This is especially important for men who still want to have children.

Can the Body Start Making Testosterone Again?

In some cases, the body can begin making its own testosterone again after stopping therapy. This process is called recovery of natural testosterone production, but it is not always fast or guaranteed.

Several factors affect how well the body recovers:

Age: Younger men often recover faster than older men.
Length of therapy: The longer someone has been on testosterone, the harder it may be to recover.
Baseline hormone levels: Men with very low levels before therapy may not recover full function.
Type and dose of therapy: Higher doses or certain delivery methods (like injections) may suppress the system more.

Recovery may take several months to over a year. Some men may never return to their original levels without medical help.

Symptoms After Stopping Therapy

Stopping testosterone therapy suddenly can cause uncomfortable symptoms. These may include:

Low energy and fatigue
Mood changes such as irritability or sadness
Trouble concentrating (sometimes called “brain fog”)
Low sex drive
Erectile problems

These symptoms happen because the body is not yet making enough testosterone on its own. This phase is sometimes called testosterone withdrawal.

Post-Cycle Therapy (PCT) and Medical Treatment

Some doctors may suggest treatments to help the body restart its natural hormone production. This approach is sometimes called post-cycle therapy, or PCT. It is more common in men who have used testosterone for bodybuilding or other non-medical reasons, but it can also be used in medical settings.

PCT may include:

Clomiphene citrate (Clomid): This medicine helps the brain send signals to the testicles again.
Human chorionic gonadotropin (hCG): This acts like LH and can help the testicles produce testosterone and sperm.
Aromatase inhibitors: These block the conversion of testosterone into estrogen, which can help raise testosterone levels.

These treatments are not always needed, and not all men respond to them. A doctor will decide based on blood tests and symptoms.

The Risk of Long-Term Dependence

Once testosterone therapy is started, many men find it hard to stop. This is because their bodies rely on the therapy to maintain hormone levels. Some men may choose to stay on testosterone for life, under a doctor’s care. This can be safe with regular monitoring, but it also means committing to a long-term treatment plan.

It is important to be aware that stopping testosterone after years of use can result in long-lasting low levels that may not fully recover.

Testosterone therapy can reduce the body’s ability to make its own testosterone and sperm. This happens because of changes in the hormone signaling system. While some men recover after stopping therapy, others may need medical help. Recovery is not always guaranteed. Understanding this process can help men make informed choices about starting and continuing testosterone therapy.

Is There a Link Between Testosterone Therapy and Sleep Apnea or Sleep Disorders?

Testosterone therapy can improve energy, mood, and sex drive. However, there is growing concern that it may affect sleep in negative ways. One of the most important issues doctors watch for is a sleep disorder called obstructive sleep apnea (OSA). This is a condition where breathing repeatedly stops and starts during sleep because the airway becomes blocked.

Some men who take testosterone may develop new sleep problems or notice their existing sleep apnea gets worse. Researchers have been studying this link to understand how testosterone affects breathing during sleep.

How Testosterone May Affect Breathing During Sleep

Testosterone is a powerful hormone that affects many systems in the body, including the brain, muscles, and respiratory system. Scientists believe that testosterone may change how the brain controls breathing at night.

The body’s breathing is partly controlled by the brainstem. This area responds to signals from the blood, such as carbon dioxide levels. When testosterone levels rise, it may reduce the brain’s sensitivity to carbon dioxide. This means the brain may not respond quickly enough when breathing slows or stops.

Another factor is muscle tone. The airway needs muscle support to stay open during sleep. If the muscles in the throat relax too much, the airway can collapse. Testosterone may affect the tone of these muscles, making airway blockage more likely during sleep.

Risk Factors for Sleep Apnea with Testosterone Use

Not all men who use testosterone therapy develop sleep apnea. However, some men are more likely to have problems than others.

Risk increases in men who already have sleep apnea but have not been diagnosed yet. In fact, many people with sleep apnea do not know they have it. The symptoms can be easy to miss or blamed on other things.

Men who are overweight or obese, have a large neck size, or snore loudly are more likely to develop or worsen sleep apnea with testosterone therapy. Older age, smoking, and alcohol use also increase risk.

Some studies have found that higher doses or longer use of testosterone are more likely to cause breathing problems at night.

What the Research Shows

A few small studies have shown that men on testosterone therapy may experience more breathing interruptions during sleep. In these studies, men who took testosterone showed more apneas and hypopneas, which are short periods where breathing slows or stops. These breathing pauses lowered oxygen levels in the blood during sleep.

Other studies did not find a strong link, so researchers believe the effect may depend on the person’s health, body weight, and dose of testosterone.

Doctors are still studying this connection. However, the possible risk is taken seriously, especially in men who already have symptoms of sleep apnea.

Common Signs of Sleep Apnea

Because many people are unaware they have sleep apnea, it’s important to know the symptoms. Some signs include:

Loud snoring
Choking or gasping during sleep
Waking up often at night
Feeling very tired during the day
Trouble focusing or headaches in the morning

If these symptoms appear after starting testosterone therapy, they should be reported to a healthcare provider.

How Doctors Monitor and Manage This Risk

Before starting testosterone therapy, a doctor may ask about sleep problems or perform a sleep study. A polysomnography is a common test used to diagnose sleep apnea.

If a man has known sleep apnea and is already using a CPAP machine (continuous positive airway pressure), testosterone may still be used carefully with monitoring. However, regular checkups are needed to watch for changes.

For men without a sleep apnea diagnosis, doctors may still check oxygen levels during sleep if symptoms appear after starting testosterone.

Balancing Benefits and Risks

Testosterone therapy can improve quality of life for men with low testosterone. But breathing problems during sleep are a serious concern. Sleep apnea can lead to high blood pressure, heart problems, fatigue, and even memory issues if not treated.

The good news is that sleep apnea is manageable. If it is caught early, treatments such as CPAP, weight loss, and changes in therapy can help.

Men who are considering testosterone therapy should be screened for sleep disorders. Those already on treatment should report any changes in sleep, energy, or mood. Careful monitoring can reduce the risks and make testosterone therapy safer.

Does Testosterone Therapy Affect Metabolism and Risk for Diabetes?

Testosterone therapy can have both helpful and harmful effects on metabolism. These effects may change depending on the person’s age, health, dose of testosterone, and how long the therapy is used. One of the most common reasons men begin testosterone therapy is to improve energy, lose weight, and feel stronger. Because of this, it is important to understand how testosterone works in the body over time—especially in relation to blood sugar, fat, and the risk of developing type 2 diabetes.

How Testosterone Affects Insulin Sensitivity

Insulin is a hormone that helps move sugar from the blood into the body’s cells. When cells stop responding to insulin properly, the body becomes insulin resistant. This leads to higher blood sugar levels and, over time, may cause type 2 diabetes. Some studies show that low testosterone levels in men are linked to higher insulin resistance. Men with low testosterone often have more belly fat, less muscle, and higher blood sugar.

Testosterone therapy may help lower insulin resistance in some men. Clinical trials have shown that testosterone can make cells more sensitive to insulin. In these men, the body uses insulin more effectively, and blood sugar levels may improve. Testosterone also helps build muscle, and more muscle can help burn sugar more efficiently. This is one way testosterone may support better blood sugar control.

However, these improvements are not guaranteed in everyone. The effects can be different depending on each person’s starting health. Men with obesity, prediabetes, or metabolic syndrome may see more benefit than men with normal weight and normal blood sugar levels.

Changes in Body Fat and Weight Control

Testosterone helps shape the male body by supporting lean muscle mass and reducing fat—especially belly fat. Men with low testosterone often gain fat in the abdominal area, which is closely linked to insulin resistance and heart disease.

When testosterone therapy is started, many men report losing some fat and gaining muscle. These changes can improve how the body processes sugar and can reduce some risk factors for diabetes. This does not mean testosterone is a weight-loss treatment, but it can help the body return to a healthier balance of fat and muscle.

Still, these benefits may take several months or even a year to appear. Weight changes may be small and must be supported by a healthy diet and regular exercise. Without these lifestyle changes, testosterone alone is less effective.

Testosterone Therapy and Type 2 Diabetes Risk

Some studies suggest testosterone therapy may lower the chance of developing type 2 diabetes in men with low testosterone. One large trial, known as the T4DM (Testosterone for the Prevention of Type 2 Diabetes Mellitus), found that testosterone therapy reduced the risk of diabetes in overweight men who had prediabetes and low testosterone. These men also followed a diet and exercise plan.

Even though this is good news, testosterone therapy is not approved as a treatment for diabetes. Doctors still recommend using lifestyle changes and medications that are proven to control blood sugar. Testosterone may be added in special cases under a doctor’s care.

It’s also important to note that in some men, testosterone therapy may raise blood sugar. This is more likely in men who already have diabetes or those taking high doses. The reason is not fully clear but may be related to changes in fat metabolism or liver function. For this reason, blood sugar levels should be checked regularly during therapy.

Monitoring Metabolic Health During Therapy

Before starting testosterone therapy, doctors usually check fasting blood sugar, hemoglobin A1C (a long-term measure of blood sugar), cholesterol levels, and body weight. These tests give a picture of a man’s metabolic health. During treatment, these same tests should be repeated every 3 to 6 months, especially if a man has diabetes or is at high risk.

Regular testing helps find problems early, such as rising blood sugar or unhealthy changes in cholesterol. If any issues appear, the dose may need to be changed, or the therapy may be stopped. Diet, exercise, and medications should always be used alongside testosterone when needed.

Testosterone therapy may improve insulin sensitivity, reduce belly fat, and support better blood sugar control in some men with low testosterone. These benefits are more likely when therapy is combined with healthy habits. However, there is also a chance of worsening blood sugar in certain people. Close monitoring and medical guidance are key to staying safe while using testosterone for long periods.

Long-Term Dermatologic and Hematologic Effects of Testosterone Therapy

Testosterone therapy can change how the body works in many ways. Some of the long-term effects are visible on the skin, while others affect the blood. Understanding these changes is important for anyone using testosterone over a long period of time. Some side effects are mild, but others may become serious if not checked regularly.

Skin Changes: Acne, Hair Loss, and Oil Production

One of the first things that might be noticed during testosterone therapy is a change in the skin. Testosterone can cause the skin’s oil glands to produce more oil. When too much oil builds up, it can clog pores and lead to acne. This is most common on the back, chest, and face. Some men may have only a few pimples, while others may develop more severe breakouts.

This type of acne is similar to what teenagers often experience during puberty. The reason is that testosterone plays a big role in puberty, and its effects on the skin are similar even in adults. Using gentle skin cleansers, oil-free products, and seeing a dermatologist if acne gets worse can help manage this problem.

Testosterone therapy can also cause hair changes. In some men, especially those who are genetically prone, testosterone can lead to male pattern baldness. This means hair starts to thin at the crown or recede from the forehead. The speed of hair loss depends on family history and the level of testosterone in the body. Once hair is lost from baldness, it usually does not grow back. Some men use medications like minoxidil or finasteride to slow down the process, but these must be discussed with a doctor.

Increased hair growth in other areas is also common. Body hair on the chest, arms, legs, or back may become thicker or grow in new places. This change can be harmless, but it may be unwanted for some.

Hematologic Effects: Increased Hematocrit and Red Blood Cells

Testosterone affects the bone marrow, which is the part of the body that makes blood cells. One of its roles is to boost red blood cell production. Over time, this can cause hematocrit levels—the percentage of blood made up of red blood cells—to rise. A small increase can be helpful, especially in men who were anemic (low in red blood cells) before therapy. But if the hematocrit goes too high, it becomes a problem.

High hematocrit makes the blood thicker than normal. Thick blood flows more slowly and increases the chance of forming blood clots. Blood clots can lead to serious events such as heart attacks, strokes, or clots in the lungs (pulmonary embolism). These events are rare but dangerous. Because of this risk, hematocrit levels must be checked before starting testosterone therapy and monitored during treatment.

Doctors usually check hematocrit every 3 to 6 months in the first year of therapy. If levels rise above 54%, the dose of testosterone may be lowered or paused. In some cases, a doctor may suggest therapeutic phlebotomy, which means removing some blood to lower the hematocrit.

High red blood cell levels may also cause symptoms like headaches, dizziness, blurred vision, or high blood pressure. If any of these symptoms occur, they should be reported to a healthcare provider right away.

Managing and Monitoring Side Effects

Regular check-ups help keep these side effects under control. Blood tests are important to make sure hematocrit stays in a safe range. Skin problems like acne and hair changes should also be mentioned to the doctor, even if they seem minor.

Good communication with the healthcare provider helps reduce risks. Most side effects can be managed if they are caught early. Skipping follow-up tests or ignoring symptoms can lead to problems later.

Testosterone therapy can offer real benefits for some men, but it comes with risks that affect both appearance and blood health. Being aware of these long-term effects helps people make safer decisions about their treatment.

Long-Term Monitoring: What Tests and Follow-Ups Are Needed?

Testosterone therapy can bring benefits, but it can also lead to changes in the body that need regular checking. Long-term use requires proper monitoring to help make sure the therapy is safe and working well. These check-ups help doctors find problems early and adjust treatment if needed. The type and timing of tests may vary, but several key checks are recommended for most men on testosterone therapy.

Testosterone Blood Levels

Blood tests are used to measure the level of testosterone in the body. This helps confirm that the treatment is giving the right amount—not too much or too little. Testosterone levels should usually be checked 2 to 3 months after starting therapy, and then every 6 to 12 months if stable.
The blood test is best done in the morning, when levels are naturally higher. It is also important to test when using long-acting forms of testosterone, such as injections, at a consistent time in the dosing cycle. For example, mid-way between injections gives a better idea of the average level.

Prostate-Specific Antigen (PSA) and Digital Rectal Exam (DRE)

The PSA test measures a protein made by the prostate. High levels may mean there are prostate problems, including cancer or benign enlargement.
Before starting testosterone therapy, men should get a baseline PSA test. PSA should then be tested at 3 to 6 months after therapy begins and then yearly.
Along with PSA, doctors may perform a digital rectal exam (DRE) to feel for prostate growth or lumps. Even though testosterone has not been proven to cause prostate cancer, it may speed up growth in men who already have cancer cells. Regular PSA testing helps catch changes early.

Red Blood Cell Count and Hematocrit

Testosterone can make the body produce more red blood cells. This can raise the hematocrit, which is the percentage of blood made up of red cells. If hematocrit becomes too high, it may increase the risk of blood clots, stroke, or heart problems.
Hematocrit should be checked before starting treatment, then again at 3 to 6 months, and at least once a year after that. If the level rises above 54%, doctors may lower the dose or stop therapy for a while. In some cases, the patient may need to donate blood (therapeutic phlebotomy) to lower the level.

Lipid Panel (Cholesterol and Triglycerides)

Testosterone therapy can change cholesterol levels, which may raise the risk of heart disease in some men. A lipid panel measures total cholesterol, LDL ("bad" cholesterol), HDL ("good" cholesterol), and triglycerides.
These should be tested before starting therapy, and then at least once a year during treatment. If cholesterol levels go up, diet, exercise, or medication may be needed.

Liver Function Tests (LFTs)

Some forms of testosterone, especially pills, may affect the liver. Liver function tests help check for liver damage or stress.
Most current testosterone therapies (like injections or gels) have little effect on the liver, but tests are sometimes still done as a safety check. These are usually part of routine blood panels done every 6 to 12 months.

Blood Sugar and Insulin Resistance

Testosterone can affect insulin sensitivity and blood sugar levels. In some men, therapy improves blood sugar control, especially if they have metabolic syndrome. In others, there may be an increase in blood sugar levels.
Tests such as fasting glucose and hemoglobin A1c can track blood sugar over time. These should be done before treatment, and then yearly or more often if the patient has diabetes or prediabetes.

Bone Density Testing

Long-term testosterone therapy may help protect bone density, especially in older men. For men at risk for osteoporosis, a DEXA scan (bone density scan) may be done every 1 to 2 years. This is especially important if testosterone was started due to low bone mass or if there is a family history of fractures.

Sleep and Breathing Checks

Testosterone therapy may worsen sleep apnea, a condition where breathing stops during sleep. Men with symptoms like loud snoring, daytime tiredness, or breathing pauses should get a sleep study.
If sleep apnea is already diagnosed, doctors may adjust treatment or work with a sleep specialist. Symptoms should be monitored regularly.

Mood and Mental Health Evaluation

Mood changes, including increased irritability or depression, can occur with hormone changes. Regular checks of emotional and mental health are important. Doctors may ask questions during follow-up visits or refer the patient to a mental health provider if needed.

Regular Follow-Up Appointments

Men on testosterone therapy should plan to visit their doctor every 3 to 6 months during the first year and every 6 to 12 months afterward. These visits allow time to review lab tests, check symptoms, and discuss side effects.
Each person may respond differently to therapy. Keeping up with regular follow-ups helps tailor the treatment plan and keeps therapy as safe and effective as possible.

Regular testing and medical follow-up are key parts of staying healthy while using testosterone therapy long term. Monitoring helps catch problems early, reduce risks, and make sure that the benefits outweigh any side effects.

Conclusion: Making Informed Decisions About Testosterone Therapy

Testosterone therapy can offer real benefits to some men. It can help with low energy, reduced muscle mass, decreased sex drive, and mood problems caused by low testosterone levels. For those with medical conditions like hypogonadism, testosterone therapy may be the right treatment. However, like any long-term treatment, it also comes with risks. Understanding both the benefits and the risks is key before starting or continuing therapy.

Long-term testosterone therapy has been shown to improve body composition. Men often see more muscle and less fat over time. Some experience better mood and energy levels, improved sexual function, and even better control of blood sugar. These effects may help some men feel more confident, active, and younger. But these benefits do not come without careful thought. Testosterone therapy changes the body’s hormone system, and over time, this can lead to problems that must be monitored closely.

One of the major risks linked to long-term testosterone therapy is related to the heart and blood vessels. Some studies show that testosterone may increase the risk of heart attacks, strokes, and blood clots in certain men, especially those who already have heart disease. Other research shows no clear risk or even some benefit. Because results are mixed, it is important to be cautious. Men on therapy often need regular checks of their blood pressure, cholesterol, and heart health to stay safe.

Fertility is another concern. Testosterone therapy can lower sperm counts and shrink the testicles. This happens because the body stops making its own testosterone when it senses high levels from outside. For men who want to have children, this side effect can be serious. In some cases, stopping therapy may reverse the changes, but not always. It is important to think about future fertility before starting therapy and to ask about ways to protect it.

Testosterone also affects the prostate. The prostate is a small gland that helps make semen. As men age, this gland often grows larger, a condition called benign prostatic hyperplasia (BPH). Testosterone therapy may make BPH worse and can raise levels of a blood marker called PSA. Doctors use PSA to watch for prostate cancer. So far, studies do not prove that testosterone therapy causes prostate cancer, but careful monitoring is needed, especially in older men or those with a history of prostate problems.

Mental health can also be affected. Some men feel better with therapy, reporting less depression or more focus. Others may notice mood swings, anger, or even sleep problems. High doses or unmonitored use can make these problems worse. This is why therapy must be managed closely by a healthcare provider. If emotional or mental changes occur, adjustments can be made to help improve safety.

Natural testosterone production is also impacted. The body may stop making its own testosterone if therapy continues for a long time. This can lead to dependence. If therapy is stopped suddenly, some men feel tired, weak, or depressed. In medical settings, doctors guide how to start and stop therapy safely. Self-medicating or stopping suddenly without a plan can make symptoms worse.

Sleep is another area where effects may appear. Some men with undiagnosed sleep apnea may find that their condition worsens on testosterone therapy. This can affect energy, focus, and heart health. Proper screening before therapy begins helps reduce these problems. If sleep issues appear, they should be evaluated and managed as part of ongoing care.

Metabolic changes are also possible. In some men, testosterone improves how the body uses insulin and manages blood sugar. This can help reduce the risk of type 2 diabetes. In others, the benefits may be limited or come with changes in weight and blood fat levels. This is why routine blood tests are needed during treatment.

Other long-term changes may include skin issues like acne or hair thinning. Testosterone can increase the number of red blood cells, which thickens the blood and raises the risk of clots. If blood counts go too high, treatment may need to be paused or adjusted.

Because of all these effects, regular follow-up is essential. Men on testosterone therapy should get routine blood tests to check hormone levels, PSA, red blood cell counts, cholesterol, and liver function. Prostate exams and heart health checks may also be recommended. These tests help catch problems early and allow for safe adjustments in treatment.

The decision to start or continue testosterone therapy should not be taken lightly. It must be based on medical testing, health history, and long-term goals. Testosterone therapy is not for everyone, and it is not a cure-all. With proper care, it can help some men feel better and live healthier lives. But close medical monitoring is needed to avoid harm. Men should work closely with their healthcare team to decide if testosterone therapy is right for them, and how to manage it safely for the long term.

Q1: What are the potential cardiovascular risks associated with long-term testosterone therapy?

Q2: Can long-term testosterone therapy affect fertility?

Q3: Does long-term testosterone therapy increase the risk of prostate cancer?

Q4: What impact does long-term testosterone therapy have on red blood cell counts?

Q5: How does long-term testosterone therapy affect mood and mental health?

Q6: Can long-term testosterone use lead to liver damage?

Q7: Does testosterone therapy increase the risk of sleep apnea?

Q8: What are the musculoskeletal effects of long-term testosterone therapy?

Q9: Can long-term testosterone therapy lead to skin problems?

Q10: How does testosterone therapy affect metabolic health over time?

From Energy to Risk: The Real Testosterone Therapy Long Term Effects Men Must Know