Testosterone therapy is a medical treatment that replaces testosterone your body isn’t producing enough of on its own. It’s prescribed to men diagnosed with hypogonadism, a condition defined by a morning blood testosterone level below 300 ng/dL combined with physical symptoms like low sex drive, fewer spontaneous erections, reduced beard growth, or shrinking testes. The FDA approves it specifically as replacement therapy for men who have at least two confirmed low testosterone readings along with these symptoms.
Who Qualifies for Treatment
Not every man with fatigue or a dip in energy has low testosterone. Diagnosis requires blood work, specifically a morning draw since testosterone peaks early in the day. The threshold most clinicians use is 300 ng/dL for total testosterone, though international guidelines from the 2024 International Consultation on Sexual Medicine place the cutoff at 350 ng/dL (12 nmol/L) for diagnosing late-onset hypogonadism in older men.
The key point is that numbers alone aren’t enough. You also need symptoms that match. The most telling signs are sexual: reduced desire, fewer morning erections, and erectile difficulties. Other common symptoms include increased body fat, loss of muscle mass, low energy, and depressed mood. If your levels are borderline but you feel fine, most guidelines recommend against treatment.
Testosterone therapy is also used in younger men with hypogonadism caused by pituitary tumors, head trauma, radiation, or genetic conditions that prevent the brain from signaling the testes to produce testosterone. It is not FDA-approved to treat low libido in women.
How It’s Delivered
There are several ways to get testosterone into your body, and the right choice depends on your lifestyle, comfort with needles, and how steady you want your levels to be.
- Injections are the most common and least expensive option. Typically 100 to 200 mg of testosterone cypionate or enanthate is injected into muscle once a week. Levels tend to spike after injection and gradually drop before the next dose, which some men notice as mood or energy fluctuations.
- Topical gels are applied daily to the shoulders or upper arms. They deliver a more consistent day-to-day level but require care to avoid transferring the gel to partners, children, or pets through skin contact.
- Subcutaneous pellets are small crystalline implants (typically 10 to 14 pellets) placed under the skin during a brief office procedure. They release testosterone steadily over three to six months, targeting a peak level between 500 and 800 ng/dL. The trade-off is a minor surgical insertion and the inability to quickly adjust your dose.
Patches, nasal gels, and oral capsules also exist but are used less frequently. Your doctor will likely start with one method and adjust based on how your blood levels respond and whether side effects develop.
What Changes and When
Testosterone therapy doesn’t produce overnight results. Different symptoms improve on different timelines, and knowing this upfront helps set realistic expectations.
Sexual desire is usually the first thing to shift, with noticeable improvement starting around three weeks and reaching its full effect by six weeks. Mood tends to follow a slower curve: depressive symptoms begin lifting between three and six weeks, but maximum improvement can take 18 to 30 weeks. Changes in body composition, including increased lean muscle and reduced fat, start appearing between 12 and 16 weeks and stabilize around six to twelve months, with small continued gains possible over years. Bone density improvements take even longer, becoming measurable after about six months and continuing for at least three years. One meta-analysis of 29 randomized trials found that testosterone therapy improved lumbar spine bone density by an average of 3.7% compared to placebo.
Risks and Side Effects
The most common side effect is a rise in red blood cell production. Your body responds to testosterone by making more red blood cells, which thickens the blood. This is measured by hematocrit, the percentage of your blood that is red blood cells. Doctors want your hematocrit to stay below 54%. If it climbs too high, the risk of blood clots increases, and your dose may need to be reduced or treatment paused.
Other side effects include acne, oily skin, breast tenderness or slight breast tissue enlargement, and worsening of sleep apnea in men who already have it. Fluid retention and ankle swelling can also occur, particularly early in treatment.
Monitoring is straightforward. The American Urological Association recommends checking testosterone levels two to four weeks after starting treatment, then every 6 to 12 months. Hematocrit should be measured on the same schedule. Men over 40 will typically have their PSA (a prostate marker) tracked as well.
Cardiovascular Safety
For years, heart risk was the biggest open question around testosterone therapy. The TRAVERSE trial, published in 2023, provided the most definitive answer to date. This was a large, randomized, placebo-controlled study of 5,246 men aged 45 to 80 who already had cardiovascular disease or were at high risk for it. The trial tracked heart attacks, strokes, and cardiovascular deaths over several years.
The result: testosterone therapy did not increase major cardiovascular events compared to placebo. There was actually a small, non-significant reduction in deaths in the testosterone group (16 fewer), though the study wasn’t designed to prove a protective effect. For men with heart disease risk factors who also have confirmed low testosterone, this trial was reassuring.
Prostate Cancer Concerns
The old fear that testosterone fuels prostate cancer has largely been set aside by modern evidence. Multiple studies of men with low testosterone treated with therapy have found no higher rates of prostate cancer compared to untreated men. The current understanding, sometimes called the saturation model, suggests that prostate cells only need a baseline amount of testosterone to grow. Once that threshold is met, adding more doesn’t accelerate cancer development.
What testosterone therapy can do is raise PSA levels, which may lead to more biopsies and therefore more cancer detection, including slow-growing cancers that might never have caused problems. This makes routine PSA monitoring important so that any rise can be interpreted in context rather than triggering unnecessary alarm. Even in men who have been treated for prostate cancer, current evidence does not show that testosterone therapy increases the risk of recurrence, though treatment in the setting of active, untreated prostate cancer remains a clear contraindication.
The Impact on Fertility
This is one of the most important and least understood consequences of testosterone therapy. Taking exogenous testosterone does not boost your fertility. It suppresses it, often dramatically.
When testosterone enters your bloodstream from an outside source, your brain reads the high levels and stops sending the hormonal signals that tell your testes to produce both testosterone and sperm. In clinical studies, 100 mg per week of injectable testosterone drove sperm counts to zero in all participants within 20 weeks. Even lower doses of 50 mg per week caused severe reductions in sperm concentration in the majority of men tested.
For men who want to have children, this is a critical consideration. The suppression is usually reversible after stopping treatment, but recovery can take months and isn’t guaranteed to return to baseline in every case. If you’re diagnosed with low testosterone but want to preserve fertility, alternative treatments exist that stimulate your body’s own testosterone production without shutting down sperm production. This is a conversation worth having before starting therapy, not after.
Who Should Not Use It
Testosterone therapy is contraindicated in men with active, untreated prostate cancer. It should also be avoided in men with untreated severe sleep apnea, uncontrolled heart failure, or a hematocrit already above 50% before treatment begins. Men actively trying to conceive should explore alternatives first, given the near-certain impact on sperm production. A baseline hematocrit, PSA (for men over 40), and at least two confirmed low morning testosterone readings are standard prerequisites before a prescription is written.