Testosterone replacement therapy (TRT) uses bioidentical testosterone, the same hormone your body produces naturally, delivered through injections, topical gels, skin patches, implanted pellets, or oral capsules. The specific form prescribed depends on how often you want to dose, how stable your blood levels need to be, and your personal preferences. Here’s how each option works and what to expect from treatment.
Who Qualifies for TRT
TRT is prescribed for men with hypogonadism, a condition where the body doesn’t produce enough testosterone on its own. The Endocrine Society sets the diagnostic threshold at a total testosterone level below 264 ng/dL, measured through a morning blood draw on at least two separate occasions. Men with levels in a gray zone (roughly 200 to 400 ng/dL) often need additional testing of free testosterone to clarify the picture. Below 150 ng/dL, deficiency is almost certain.
The underlying cause matters. Primary hypogonadism means the testes themselves are the problem, often from injury, infection, or a genetic condition. Secondary hypogonadism means the signaling hormones from the brain aren’t doing their job, which can stem from obesity, pituitary disorders, or certain medications. Both types are treated with testosterone, though secondary hypogonadism sometimes responds to other approaches that restart the brain’s signaling instead.
Injectable Testosterone Esters
Injections are the most common and cost-effective form of TRT. The testosterone molecule is attached to a chemical “tail” called an ester, which controls how slowly the hormone releases into your bloodstream after injection. Three esters dominate the market:
- Testosterone cypionate is the most widely prescribed in the United States. It’s long-acting, typically injected once every one to two weeks, and provides relatively stable levels between doses.
- Testosterone enanthate is the most popular option worldwide. It behaves almost identically to cypionate with a similar injection schedule of every one to two weeks.
- Testosterone propionate is short-acting and requires injections every two to three days. It’s rarely used for ongoing TRT because of the frequent dosing, but some men prefer it for tighter control over their levels.
Many men on cypionate or enanthate split their dose into two smaller injections per week rather than one large one. This keeps blood levels more stable and can reduce side effects like mood swings or spikes in estrogen.
Gels, Patches, and Nasal Gels
Topical testosterone absorbs directly through the skin and provides steady daily dosing without needles. You apply the clear gel once a day, usually to the shoulders, upper arms, or abdomen. The main drawback is the risk of transferring testosterone to other people through skin contact, so you need to wash your hands thoroughly and cover the application site with clothing.
Skin patches work similarly but use a different delivery system. You apply one patch daily, typically between 8 p.m. and midnight, to an area that won’t get sweaty or compressed. Some men find patches irritating to the skin over time.
A nasal gel option exists as well. It’s applied three times a day in each nostril, spaced six to eight hours apart. This avoids the skin-transfer issue entirely, though the frequent application schedule is a trade-off.
Pellets and Oral Capsules
For men who want the least day-to-day involvement, subcutaneous pellets are an option. A provider implants small testosterone pellets under the skin, usually in the buttock area, every three to six months. Your body absorbs the hormone gradually into the bloodstream. The downside is that if you experience side effects, you can’t simply stop dosing; the pellets are already in place.
Oral testosterone has a complicated history. Older oral formulations were processed through the liver and carried serious risks, including liver tumors and liver damage. A newer oral capsule (testosterone undecanoate, sold as Jatenzo) was designed to avoid these problems. It’s absorbed through the lymphatic system rather than passing directly through the liver, and the FDA label specifically notes it is not known to cause the liver complications associated with older oral steroids. It’s taken twice daily with food.
What TRT Does to Your Body Over Time
The effects of TRT don’t arrive all at once. They roll in over weeks and months in a fairly predictable sequence.
Energy and mood tend to improve first. Within the first two weeks, many men notice reduced fatigue and a slight uptick in motivation and focus. By weeks three to four, stress feels more manageable and irritability typically drops. Mood continues stabilizing through weeks seven and eight, and by the end of the third month most men describe a consistent, predictable baseline.
Sexual function follows a similar but slightly slower curve. Morning erections and sexual interest often pick up around weeks three to four. Erectile function and desire continue improving through weeks five to eight, then level off into a more reliable pattern by weeks nine through twelve.
Body composition changes take longer. You’re unlikely to notice anything in the mirror during the first month. Around weeks seven to eight, clothes may start fitting differently, particularly around the waist and chest. Meaningful shifts in fat loss and lean muscle gain typically begin taking shape around week twelve and continue stabilizing over six to twelve months. Bone density improvements happen on an even longer timeline, measured in months to years rather than weeks.
Fertility and Testicular Changes
This is one of the most important things to understand before starting TRT: exogenous testosterone almost always suppresses sperm production. When your body detects testosterone coming from an outside source, it dials down the hormonal signals that tell the testes to make sperm. The result is either a very low sperm count or no sperm in the semen at all.
The testes need internal testosterone concentrations many times higher than what circulates in the blood to produce sperm. TRT raises blood levels but actually lowers the concentration inside the testes, which is why fertility drops. If you stop testosterone, sperm production typically recovers within about three months, and no permanent damage is expected. But if preserving fertility is a priority, this needs to be part of the conversation before you start.
Some providers prescribe additional medications alongside TRT to keep the testes functioning. Clomiphene citrate blocks estrogen’s feedback signal to the brain, which keeps the brain sending its own stimulating hormones to the testes. This helps maintain testicular size and sperm production while still getting the benefits of supplemental testosterone. The combination can provide higher overall testosterone levels from the external dose while preventing the testes from shutting down completely.
Blood Work and Ongoing Monitoring
TRT is not a set-it-and-forget-it treatment. Regular blood work is essential to make sure your levels are in range and that you’re not developing side effects. One of the most important markers to track is hematocrit, the percentage of your blood made up of red blood cells. Testosterone stimulates red blood cell production, and if hematocrit climbs too high, your blood becomes thicker and harder to pump. The American Urological Association recommends keeping hematocrit below 54%, with a baseline measurement before starting treatment to confirm you’re under 50%.
Hematocrit and hemoglobin are checked every six to twelve months, or more often if previous values were trending upward. If your hematocrit rises too high, your provider will typically lower your dose or adjust your injection frequency. Testosterone levels themselves are rechecked periodically to fine-tune dosing, along with estrogen levels and other markers that can shift during treatment.