TRT is a medical treatment
Testosterone replacement is a prescription treatment for diagnosed testosterone deficiency. Symptoms such as fatigue or poor recovery have many possible causes; a clinician needs to assess them. Trial findings in men with confirmed deficiency do not establish benefits for healthy men seeking better training results.
I'm on TRT, prescribed and monitored by my doctor. I don't publish doses or my results.
Why I looked into it
I started reading about TRT because recovery felt slower and sleep was not restoring me despite consistent training. I wanted evidence rather than guesswork. This is a reason for reading the research, not a recommendation to use a compound.
What the Research Actually Says
Testosterone contributes to muscle and bone function and red blood cell production. Testosterone supplied from outside the body feeds back on the hypothalamic-pituitary-gonadal (HPG) axis, suppressing the signals that drive natural testosterone production and sperm production. Some testosterone is converted to oestrogen by aromatase. These are reasons for clinical assessment, not a rationale for adjusting hormones without a prescriber.
Haematocrit is the proportion of blood volume occupied by red blood cells. Testosterone can raise it; an excessive rise increases blood viscosity and is a safety concern. Lipids, including LDL, HDL and triglycerides, and blood pressure also matter to cardiovascular assessment. The Zitzmann et al. expert statement discusses assessment and monitoring alongside the TRAVERSE evidence. This is an explanation of why monitoring matters, not a testing schedule or treatment protocol.
The Biggest Trial: What TRAVERSE Actually Found
For years the honest answer to "is TRT safe for your heart?" was that nobody had run a trial big enough to say. That changed in 2023. TRAVERSE was a randomised, double-blind, placebo-controlled trial of 5,246 men aged 45 to 80 who had symptoms of low testosterone, two fasting testosterone readings below the reference range, and either existing cardiovascular disease or a high risk of it. Half got a daily transdermal testosterone gel, half got a placebo gel. Mean follow-up was 33 months. It was published in the New England Journal of Medicine: Lincoff AM et al., Cardiovascular Safety of Testosterone-Replacement Therapy, N Engl J Med 2023;389(2):107-117 (PMID 37326322).
The headline result: a major cardiovascular event happened in 7.0% of the testosterone group and 7.3% of the placebo group. Testosterone was non-inferior to placebo on cardiac events. That is the reassuring part, and it is a genuinely important finding given how long the opposite was assumed.
The part that gets left out of the reassuring summaries is the rest of the results. The testosterone group had a higher incidence of atrial fibrillation, acute kidney injury and pulmonary embolism. So the fair reading is not "TRT is safe", it is "TRT did not raise heart attack and stroke risk in a high-risk population, and it did raise some other things you should be monitored for". Monitoring decisions belong with the prescribing clinician.
I looked for an Irish cohort study on this and there is not one. The nearest thing to a European read on it is a position statement from the European Expert Panel for Testosterone Research, which reviews TRAVERSE alongside earlier trials and meta-analyses and lands on the same place: reasonable safety in appropriately selected patients, with careful monitoring of haematocrit specifically (Zitzmann M et al., Andrology 2026;14(1):294-302, PMID 40372318).
Two things worth holding on to before anyone reads that as a green light. TRAVERSE enrolled men with diagnosed, symptomatic, biochemically confirmed low testosterone, so it says nothing about a healthy man taking testosterone to train harder. And "non-inferior on cardiac events over 33 months" is not the same as "safe over 30 years". The data is better than it was. It is not finished.
Sport status: Exogenous testosterone is prohibited at all times under S1.1 of the WADA 2026 Prohibited List. A prescription does not itself establish anti-doping permission; athletes should check the therapeutic use exemption requirements with their anti-doping organisation.
Summary
TRAVERSE studied men with symptoms and confirmed low testosterone, not healthy men seeking performance improvements. Its cardiovascular result does not establish lifelong safety. Speak to a GP about symptoms or treatment questions.