Hormone replacement therapy for men is a medical treatment that restores testosterone to normal levels when the body can no longer produce enough on its own. The clinical term is testosterone replacement therapy, or TRT, and it’s prescribed when a man’s total testosterone falls below 300 ng/dL and he has symptoms like low sex drive, fatigue, loss of muscle mass, or mood changes. It’s not a one-size-fits-all treatment, and it requires ongoing blood work and monitoring.
How Low Testosterone Gets Diagnosed
Testosterone levels fluctuate throughout the day, peaking in the morning and dropping later. That’s why blood draws are typically done before 10 a.m. The American Urological Association defines low testosterone as a total level below 300 ng/dL, confirmed on at least two separate morning blood tests. A single low reading isn’t enough for a diagnosis.
Free testosterone, the portion not bound to proteins in the blood, is sometimes measured as well. But it’s not the primary diagnostic tool. Free testosterone testing is most useful when total testosterone falls in the gray zone between 230 and 317 ng/dL. Below 231, free testosterone adds little to the picture. Above 317, deficiency is unlikely. The symptoms matter just as much as the number: if your levels are borderline but you feel fine, treatment may not be recommended.
What Testosterone Does in the Body
Testosterone binds to androgen receptors found throughout the body, including in muscle, bone, fat tissue, and the brain. Once it locks onto a receptor, it activates gene expression that promotes and maintains male traits and reproductive function. In bone, androgen receptors are present in the cells responsible for both building and breaking down bone tissue, which is why low testosterone contributes to bone loss over time. In muscle, it stimulates protein synthesis, which supports both muscle mass and strength. It also plays a role in red blood cell production, mood regulation, and sexual function.
Replacing testosterone from an outside source works the same way. The exogenous hormone binds to the same receptors and triggers the same downstream effects. But there’s a trade-off: when the body detects adequate testosterone coming from an external source, it reduces its own production. This has significant implications, especially for fertility.
How TRT Is Administered
There are several ways to deliver testosterone, each with different schedules and considerations.
- Injections are the most common and least expensive option. Subcutaneous injections are typically given once a week, starting around 75 mg. Intramuscular injections using testosterone cypionate or enanthate follow a similar weekly or biweekly schedule. The American College of Physicians recommends considering injections over other forms when starting therapy, largely due to lower cost with comparable effectiveness.
- Topical gels are applied daily to the shoulders or upper arms. They deliver a steady dose but carry the risk of transferring testosterone to others through skin contact.
- Patches are worn on the skin and changed daily. They tend to cause skin irritation more than other methods.
- Subcutaneous pellets are implanted under the skin every three to six months, offering the longest interval between doses but requiring a minor in-office procedure each time.
The choice depends on your lifestyle, comfort with needles, budget, and how your body responds. Dosing is adjusted based on follow-up blood work rather than fixed from the start.
When You’ll Notice Changes
Testosterone therapy doesn’t produce overnight results. The timeline unfolds gradually over weeks and months, and different symptoms improve at different rates.
In the first two weeks, some men notice a slight uptick in motivation and focus, along with reduced fatigue. Libido may start to increase, but it’s usually subtle. By weeks three and four, stress tolerance and irritability tend to improve, and many men report the return of morning erections and increased sexual interest.
Weeks five through eight bring more consistent mood stability and clearer improvements in both desire and sexual function. Body composition changes start showing up around weeks seven and eight. Clothes may fit differently, particularly around the waist and chest, though you won’t see dramatic physical transformation this early.
By weeks nine through twelve, mood and libido typically level off at a stronger, more predictable baseline. Fat loss and lean muscle gains become more visible, especially with consistent strength training and good nutrition. Research shows that body composition changes really take shape around week twelve and continue stabilizing over the following six to twelve months. If after six to twelve months of treatment your symptoms haven’t meaningfully improved despite your testosterone levels being in the normal range, guidelines recommend discontinuing therapy.
Required Blood Work and Monitoring
TRT isn’t a “set it and forget it” treatment. Regular lab work is essential to keep the therapy safe and effective.
After starting, testosterone levels, hemoglobin, hematocrit, and PSA (a prostate marker) are checked at three to six months, then again at twelve months. Timing of the blood draw matters: if you’re on weekly injections, the draw should happen midway between doses (around day three or four) to avoid catching a peak or trough. For gels, the best window is two to eight hours after application, once you’ve been using it consistently for at least a week.
The goal is to keep total testosterone below 900 ng/dL and hematocrit below 51%. If hematocrit climbs above 54%, testosterone must be stopped. PSA is checked at baseline, at twelve months, and then annually. A PSA jump greater than 1.4 ng/mL within a year, or a level above 4 ng/mL at any point, warrants a urology referral. Estradiol, a form of estrogen, is tested if you develop breast tenderness or tissue growth, since testosterone can convert to estrogen in the body.
Side Effects and Safety Concerns
The most common side effect of TRT is an increase in red blood cell production, a condition called erythrocytosis. All forms of testosterone cause a measurable rise in hematocrit, the percentage of blood volume occupied by red blood cells. A systematic review of randomized trials found that gels raise hematocrit by about 3%, intramuscular injections of testosterone cypionate or enanthate by about 4%, and patches by about 1.4%. While these increases are modest, they matter because thicker blood raises the risk of blood clots and cardiovascular events.
Cardiovascular safety has been a long-standing concern. The TRAVERSE trial, the largest randomized study to date on this question, enrolled over 5,000 men with cardiovascular risk factors and followed them for an average of about 22 months. The conclusion: testosterone therapy was noninferior to placebo for major adverse cardiac events, meaning it didn’t increase heart attack or stroke risk over that period. That said, the study had important limitations. Over 60% of participants in both groups stopped treatment, and about 18% were lost to follow-up. The study also ran for a shorter duration than originally planned. So while the results are reassuring in the medium term, they don’t provide a definitive answer about long-term cardiovascular safety spanning five or more years.
The Impact on Fertility
This is one of the most important and often overlooked consequences of TRT. When you introduce testosterone from an outside source, your brain registers that levels are sufficient and stops signaling the testes to produce their own. This shuts down sperm production. About 65% of men with normal sperm counts who go on testosterone develop azoospermia, a complete absence of sperm, within four months.
For men who want to have children in the future, this makes TRT a poor choice unless fertility-preserving medications are used alongside it. Some protocols use human chorionic gonadotropin (hCG) to keep the testes active during treatment, and recovery of sperm production after stopping TRT is possible but not guaranteed. If future fertility is important to you, this needs to be part of the conversation before starting therapy.
Who Should Not Take TRT
Several conditions make testosterone therapy unsafe. Active prostate cancer and breast cancer are absolute contraindications. So are uncontrolled elevated red blood cell counts, unevaluated PSA levels above 4 ng/mL, severe untreated obstructive sleep apnea, and poorly controlled heart failure. Men who have had a heart attack, stroke, or blood vessel procedure within the last four months should not start therapy. A history of unexplained blood clots or a clotting disorder also rules it out.
Severe liver disease, kidney failure, and severe urinary symptoms related to prostate enlargement are additional disqualifiers. And as noted above, men who want to preserve fertility should explore alternatives before committing to standard TRT.