Testosterone plays an important role in men’s health. It affects muscle mass, energy, mood and sexual function. But its role goes beyond sex drive. Testosterone also supports bone strength, red blood cell production in the bone marrow and overall well-being.

It is produced mainly in the testicles and regulated by signals from the brain. When levels are balanced, testosterone helps the body function normally. When levels drop too low, it can affect both physical and emotional health.

What Does Testosterone Do?

Testosterone is often called the “male sex hormone,” but it has many functions in the body.

It helps:

• Build and maintain muscle mass
• Support bone density
• Produce sperm
• Regulate mood and energy
• Stimulate red blood cell production

Low levels of testosterone can lead to fatigue, reduced strength, and changes in mood and motivation.

What Is Testosterone Replacement Therapy?

Testosterone replacement therapy (TRT) is a medical treatment used to restore low levels of testosterone in men. It is designed for those diagnosed with male hypogonadism, a condition in which the body does not make enough testosterone.

TRT is intended for men who have both symptoms and consistently low levels confirmed through testing. It is not recommended as a general treatment for normal aging or low energy alone.

“Testosterone therapy isn’t a quick fix for feeling tired or getting older. Symptoms like fatigue, low energy or low libido can be caused by many conditions, including sleep apnea, depression, thyroid disorders and chronic illness,” says Dr. Amarasekera. “Before starting testosterone therapy, it’s important to rule out these causes and confirm a diagnosis of low testosterone with proper lab testing.”

What Are the Symptoms of Low Testosterone?

Low testosterone can cause a range of symptoms, including:

• Low energy or fatigue
• Reduced muscle mass
• Decreased sex drive
• Erectile dysfunction
• Mood changes, such as depression or irritability
• Difficulty concentrating

Some men may also notice increased body fat, reduced strength or changes in hair growth patterns. These symptoms can affect daily life and should prompt a conversation with your doctor.

How Is Low Testosterone Diagnosed?

Diagnosis begins with a discussion of symptoms and health history. A blood test is required to measure testosterone levels, usually in the morning when levels are highest.

Doctors typically confirm the diagnosis with two separate blood tests showing low levels of testosterone, along with symptoms consistent with hypogonadism.

Careful diagnosis is essential because many men are started on therapy without proper testing or clear indications, which can lead to unnecessary treatment.

What Is Considered Low Testosterone?

Normal testosterone levels typically range from about 300 to 1,000 nanograms per deciliter (ng/dL). Levels below 300 ng/dL, along with symptoms, may indicate low testosterone.

However, “normal” can vary by lab and individual factors, so results should always be interpreted by a doctor.

What Causes Testosterone Levels To Decline?

Testosterone levels can decline due to several factors, including:

• Aging
• Obesity
• Chronic illness
• Some medications, such as opioids and corticosteroids
• Poor sleep or sleep apnea

Lifestyle factors like stress, lack of exercise and poor diet can also contribute. Some of these causes are reversible with healthy changes.

Aging vs. Hypogonadism

A gradual decline in testosterone is a normal part of aging, especially in older men. However, male hypogonadism is a medical condition with a clear cause and more significant hormone deficiency.

This distinction is important because treatment decisions should be based on medical need, not age alone.

Benefits of TRT

TRT may help improve symptoms, such as:

• Energy levels
• Mood
• Sexual function
• Muscle mass

Some men notice improvements in libido within a few weeks. Physical changes, such as increased muscle mass, may take longer. However, expectations should be realistic. TRT can improve certain symptoms but is not a cure-all for fatigue, aging or general wellness.

What Improves the Most?

Sexual symptoms and energy levels are often the first to improve. Changes in muscle mass and strength develop over time.

Not all symptoms improve equally, and the response to testosterone therapy can vary.

What Are the Risks and Side Effects?

Like any medical treatment, testosterone replacement therapy can have side effects. These may include:

• Acne or oily skin
• Fluid retention
• Breast tenderness or enlargement
• Reduced fertility
• Increased red blood cell count

An elevated red blood cell count can increase blood thickness and may raise the risk of complications, such as blood clots, which is why routine monitoring is essential during treatment.

When you take testosterone from outside the body, your body senses that hormone levels are adequate. Because of this, the brain sends fewer signals that normally tell the testes to work. As a result, the testes slow down or stop making testosterone and sperm. Depending on the dose, sperm counts may decline significantly — or even drop to zero — within weeks to months of starting therapy.

TRT may also worsen sleep apnea in some people.

Understanding these potential risks is important when considering whether TRT is the right option for you.

Does TRT Increase Your Risk of Cancer or Heart Problems?

Research shows that TRT does not appear to cause prostate cancer. However, prostate cancer cells are often sensitive to testosterone, meaning the hormone can influence their growth. In some cases, testosterone therapy may increase prostate activity or raise prostate-specific antigen (PSA) levels, which can lead to earlier detection of previously undiagnosed cancer. For this reason, careful screening and monitoring are recommended before and during treatment.

The relationship between TRT and heart disease is still being studied. For most people, treatment is considered safe when used under medical supervision and personal risk factors are taken into account.

Who Should Avoid TRT?

TRT may not be appropriate for men with certain health conditions, including:

• Prostate or breast cancer
• Untreated sleep apnea
• High red blood cell count
• Severe heart disease

A complete medical evaluation is necessary before starting treatment.

Should Women Take TRT?

Testosterone plays a role in men and women, but levels are much lower in women. Because of this, TRT is not commonly used in women and is only recommended in specific situations.

Some women may have low testosterone levels due to aging, removal of the ovaries or certain medical conditions. In some circumstances, a doctor may prescribe low-dose testosterone to help with symptoms, such as reduced sexual desire.

TRT is not approved by the U.S. Food and Drug Administration (FDA) for routine use in women in the United States, but in select cases, it may be prescribed off-label. Its long-term safety in women is still being studied. Because of these risks, treatment should only be considered after a careful medical evaluation. For most women, other treatments are usually recommended first.

What Are the Different Forms of Testosterone?

There are several forms of TRT:

• Gels or creams applied daily
• Injections given weekly or every two weeks
• Skin patches applied daily
• Pellets placed under the skin by a medical professional every three to six months
• Oral testosterone tablets typically taken twice daily

Each option delivers different amounts of testosterone and varies in convenience and dosing consistency. The best treatment depends on several factors, including:

• Personal preference
• Lifestyle
• Cost and insurance coverage
• Medical history

Treatment decisions are made through shared decision-making between you and your doctor, taking into account goals, risks and expected outcomes.

What Monitoring Is Required?

Regular monitoring is a key part of TRT. Your doctor will track:

• Levels of testosterone
• Red blood cell count
• Prostate health

Ongoing follow-up ensures that treatment is working and helps detect any side effects early.

How Often Are Follow-Up Visits Needed?

Follow-up visits are usually more frequent during the first year of treatment. Once levels are stable, visits may occur once or twice a year. Blood tests are done regularly to confirm safe and effective dosing.

Common markers checked in blood tests include:

• Testosterone levels
• Hematocrit (red blood cell count)
• Prostate-specific antigen (PSA)

How Does TRT Affect Fertility?

TRT can lower sperm count and affect fertility. When testosterone is introduced from outside the body, such as through medication, injections or gel, it signals the brain to reduce natural hormone production. This decreases stimulation of the testes, which can lead to reduced sperm production — sometimes significantly.

Fertility is an important consideration, especially for younger men who may want to have children. In these cases, TRT may not be the best option. Some alternative treatments can help stimulate the body’s natural testosterone production without suppressing sperm production and may be more appropriate for preserving fertility. These include:

• Selective estrogen receptor modulators (SERMs)
• Human chorionic gonadotropin (hCG)
• Aromatase inhibitors

“Many men don’t realize that testosterone therapy can lower sperm counts, sometimes significantly,” says Dr. Amarasekera. “If fertility is a goal, it is important to let your care team know so the right treatment can be selected to help improve testosterone without compromising fertility.”

Can Lifestyle Changes Help?

Healthy habits can support testosterone levels and overall health. These include:

• Strength training two to three times per week
• Getting seven to nine hours of sleep each night
• Avoiding or limiting alcohol
• Maintaining a healthy weight
• Managing stress

Lifestyle improvements are often recommended before considering testosterone therapy.

“Lifestyle changes like better sleep, exercise and weight loss can improve testosterone levels and overall health, sometimes without medication,” says Dr. Amarasekera.

What Does TRT Cost?

The cost of TRT varies depending on the treatment type and insurance coverage. Some plans cover therapy when there is a clear medical need. Costs may include medication, doctor visits and lab testing.

Is TRT a Long-Term Treatment?

TRT is often a long-term therapy. If treatment is stopped, testosterone levels typically return to previously low levels. Decisions about continuing or stopping therapy should be made with your doctor. Your doctor will also monitor you regularly to make sure the treatment is helping and not negatively affecting your health.

What Should You Consider Before Starting TRT?

Before starting testosterone replacement therapy, it is important to:

• Confirm the diagnosis with proper testing.
• Understand the benefits and risks.
• Consider personal health conditions.
• Work closely with a qualified physician, such as a primary care physician, urologist or endocrinologist.

TRT can improve quality of life, but it requires careful evaluation and ongoing monitoring.

When Should You See a Doctor?

Consider talking to your doctor if you experience:

• Persistent fatigue or low energy
• Reduced sex drive or erectile issues
• Loss of muscle or increased body fat
• Depression, irritability or brain fog

These symptoms can have many causes, so proper evaluation is important before considering treatment.