TRT: what testosterone therapy is actually proven to do

Testosterone replacement therapy sits in an unusual spot: it’s a genuinely effective, well-studied, FDA-approved treatment — and one of the most over-prescribed and over-hyped therapies in men’s health. The two facts coexist. The key to reading TRT honestly is separating what it’s proven to do, for whom, from the anti-aging marketing built around it.

Who TRT is actually for

TRT treats hypogonadism — clinically low testosterone with symptoms. The Endocrine Society guideline is explicit: diagnose it only in men with “symptoms and signs consistent with testosterone deficiency and unequivocally and consistently low serum testosterone,” confirmed by repeating a morning blood test.^[1] That last part matters: a single borderline reading isn’t a diagnosis. And crucially, TRT is not endorsed for men with low-normal testosterone, vague fatigue, or simple aging — the exact population the wellness market targets hardest.

What it actually does

The best evidence on benefits is the NIH-funded Testosterone Trials, which treated 790 men aged 65+ with low testosterone and symptoms for a year. The results were a study in nuance: testosterone significantly improved sexual activity, desire and erectile function, and produced slightly better mood and fewer depressive symptoms — but it had no significant benefit for vitality, and only a marginal effect on walking distance.^[2] The authors’ own summary: a “moderate” benefit for sexual function, some benefit for mood, and none for vitality or walking.^[2]

Is it safe for the heart?

For years the biggest open question was cardiovascular safety. The TRAVERSE trial— 5,246 hypogonadal men with existing or high cardiovascular risk — was designed to answer it. Major adverse cardiac events occurred in 7.0% of the testosterone group versus 7.3% on placebo (hazard ratio 0.96), meeting the bar for non-inferiority.^[3]In plain terms: in this high-risk population, TRT did not increase heart attacks, strokes or cardiovascular death. That’s reassuring — with one honest caveat: the same trial saw a higher incidence of atrial fibrillation, pulmonary embolism and acute kidney injury in the testosterone group, which we cover in the side-effects breakdown.^[3]

The fertility trade-off

One consequence is non-negotiable physiology: exogenous testosterone suppresses your own production. By supplying testosterone from outside, TRT signals the brain to dial down LH and FSH, which reduces sperm production — an effect that is usually reversible but very real.^[4] For a man who wants to preserve fertility, this is the decisive issue, and the reason enclomiphene exists: it raises your own testosterone while keeping sperm production intact. We lay the choice out in enclomiphene vs TRT.

The forms it comes in

TRT isn’t one product. It’s delivered as injections (testosterone cypionate or enanthate, intramuscular or subcutaneous), transdermal gels and patches, pellets implanted under the skin, a nasal gel, and newer oral capsules.^[5] The route affects dosing rhythm, convenience, and even side effects — injections raise red-blood-cell counts more than patches, for instance — which is part of why provider choice and monitoring matter.

The honest bottom line

For a man with genuine, confirmed hypogonadism, TRT is an effective, approved, and — per TRAVERSE — cardiovascularly reassuring therapy, with real benefits for sexual function and mood.^[2][3]For a man with normal or low-normal testosterone chasing energy or anti-aging, it’s the wrong tool: the benefits the marketing promises aren’t the ones the trials found, and the trade-offs (fertility, monitoring) are real. The right first step is an honest diagnosis — see how to get TRT, the side-effects and cost guides, and our comparison of TRT providers.