Testosterone therapy didn't raise heart attacks or prostate cancer in a 5,200-man trial

Evidence check, September 28, 2026

The claim: "Testosterone therapy doesn't cause heart attacks; the TRAVERSE trial settled it."

Our grade: Solid. In a randomized trial of 5,204 men with truly low testosterone, heart attacks, strokes and heart deaths were the same on testosterone and placebo (7.0% vs 7.3%), and prostate cancer was no more common (12 vs 11 men). It's for men whose blood tests are low twice, not for a normal level, and it has real side effects to watch.

Tom is 52. For a year he's been tired by mid-afternoon, his sex drive has faded, and his weekend hikes feel harder than they should. His doctor ran a blood test: testosterone 260. A friend on testosterone says it gave him his life back. An older friend warns that it causes heart attacks and prostate cancer.

Would testosterone therapy make Tom's heart or prostate the price of feeling better?

For years nobody knew. In 2015 the FDA made testosterone labels warn of a possible higher risk of heart attacks and strokes [11]. Then came the biggest trial ever done on the question, and its prostate results.

What TRT is, and where the testosterone comes from

TRT (testosterone replacement therapy) means using testosterone to bring a low level back into the normal range. It comes as a daily gel on the skin, a patch, a pill, pellets under the skin or a shot every week or two.

The testosterone isn't taken from animals or people. It's made in factories from plant sterols, fat-like molecules in soybeans and wild yams. In the 1940s the chemist Russell Marker found how to turn diosgenin, a sterol from Mexican yams, into the hormone progesterone, and that started the modern hormone industry [12]. Today bacteria turn soybean sterols into a close cousin of testosterone, and one more step finishes the job [13]. The result is the same molecule your testes make. Chemists first made testosterone in the lab in 1935, and Adolf Butenandt and Leopold Ruzicka shared the 1939 Nobel Prize for that work [14].

The "from cadavers" story is about a different hormone. Until 1985 human growth hormone was taken from the pituitary glands of people who had died. That year some who had received it were found to have Creutzfeldt-Jakob disease, a fatal brain infection, and a lab-made version replaced it [15].

Where the claim came from

When the TRAVERSE trial came out in 2023, it answered the heart question the FDA had asked drugmakers to test [1]. In February 2025 the FDA took the heart-attack language off testosterone's boxed warning and added the trial's results to every label [11]. On Peter Attia's podcast in July 2024, urologist Ted Schaeffer walked through its prostate results and said there was no evidence that testosterone replacement speeds up someone's prostate cancer [10].

Clue one: the heart held steady

TRAVERSE randomly split 5,246 men aged 45 to 80 into two groups: testosterone gel or a placebo gel [1]. Every man had symptoms, two morning blood tests under 300 ng/dL, and heart disease or a high risk of it. That's a group where any heart harm should show up fast. Doses were adjusted to keep testosterone between 350 and 750.

After an average of 33 months of follow-up, a heart attack, stroke or heart death had happened to 182 men on testosterone (7.0%) and 190 on placebo (7.3%) [1].

A 2024 review for the UK's health research agency pooled 35 randomized trials with 5,601 men and found the same: heart and stroke events in 7.5% on testosterone and 7.2% on placebo [9].

Clue two: the prostate held steady too

The worry comes from how prostate cancer is treated: shutting testosterone down slows it. So wouldn't adding testosterone speed it up?

TRAVERSE tracked this closely [2]. Prostate cancer was found in 12 men on testosterone and 11 on placebo, about 0.5% in each group [1]. High-grade cancers, the kind more likely to spread, were 5 against 3, too few to tell apart. Biopsies, urinary problems and prostate surgery were also no more common. PSA, the blood marker used to screen for prostate cancer, rose a little more on testosterone: 0.20 against 0.08 ng/mL.

One reason may be that the prostate "fills up" on testosterone at fairly low levels, so raising a low level to normal adds little more push. Schaeffer explains it this way on the podcast [10]. It's a theory; the trial result is the evidence.

There's a catch. Men with a PSA over 3, prostate nodules or past prostate cancer weren't allowed in [2]. So the answer is for men who were screened first, the way guidelines already say to do [7].

Clue three: it helps, and it has real costs

In TRAVERSE, 1,161 men with low sex drive had more sexual activity and desire on testosterone, lasting 2 years, but erections didn't improve [3]. Mood and energy got a little better in the whole trial [4]. Of 815 men who started with anemia (too few red blood cells), 41% were cured by 6 months on testosterone against 28% on placebo [5]. In an earlier NIH-funded trial of 790 men 65 and older, testosterone improved sex drive, erections and mood for a year, but not tiredness [6].

The costs, from the same randomized trials:

• More atrial fibrillation, an irregular heartbeat: 3.5% against 2.4% [1].
• More blood clots in the lungs: 0.9% against 0.5% [1].
• More acute kidney injury: 2.3% against 1.5% [1].
• More fractures, not fewer: 3.5% against 2.5%, even though testosterone makes bones denser [8].
• Thicker blood. A pooled analysis of 4 trials found about 8 times the risk of too many red blood cells, which is why doctors check a blood count [16].
• Higher blood pressure. The FDA added a warning for every product in 2025 [11].
• It shuts down sperm. In a World Health Organization study of 399 men in 9 countries, weekly testosterone shots worked as male birth control. Sperm came back after the shots stopped [17].
• It didn't prevent diabetes in men with prediabetes [18].

So back to Tom. If his level is low on a second morning test and his PSA and blood count are fine, testosterone won't cost him his heart or his prostate. It may well bring back his sex drive and some energy. What he should watch is his heart rhythm, his blood count, his blood pressure, and whether he still wants children.

Our grade

The case for the other side: TRAVERSE used gel at normal doses in men with truly low levels, so it says nothing about high doses or men with normal testosterone. Many men stopped their gel early; the average time on treatment was 22 months, and Schaeffer points out how many dropped out [10]. That could hide a harm that builds slowly. The prostate result rests on few cancers, and the trial ran only a few years. The fracture and atrial fibrillation findings were surprises. AbbVie, which makes testosterone gel, helped fund TRAVERSE [1].

What would change the grade: a trial that follows men on testosterone for 10 years or more, or one in men with normal levels.

What this means for you

TRT treats low testosterone with symptoms. It isn't an anti-aging drug for men with normal levels, and no trial has tested it that way. Guidelines say to confirm a low level with two fasting morning tests, and to find the cause before starting [7].

If you're 18 to 39

• Low testosterone at your age has a cause worth finding first: sleep apnea, weight, medicines, or a problem with the pituitary gland. Ask your doctor to look.
• If you may want children, don't start testosterone. It can stop sperm production, and guidelines advise against it if you're planning a family soon [7]. Ask about treatments that raise your own testosterone instead.

If you're 40 to 64

• If you're tired, have little sex drive, and two morning tests are below about 300 ng/dL, TRT is a reasonable thing to ask about. The heart worry is largely off the table.
• Get a PSA and a blood count before you start, and again in the first year [7].
• Check your blood pressure, and tell your doctor about palpitations (a racing or skipping heart) or a swollen, painful leg.

If you're 65 or older

• The same benefits showed up after 65: better sex drive and mood [6]. Don't expect it to fix tiredness or walking speed.
• Testosterone made bones denser but didn't prevent fractures. Keep lifting weights and ask about proven bone medicines if your bones are thin [8].
• If you've had prostate cancer, that's a conversation with your urologist; these trials didn't include you.

What's next

This is the first article in our new Hormones series. Next: menopausal hormone therapy, and what the newer studies say about it. If you're lifting to hold on to muscle, see how much protein you need at your age.

Sources

1. Lincoff AM, Bhasin S, Flevaris P, et al. Cardiovascular safety of testosterone-replacement therapy. N Engl J Med, 2023. 5,246 men aged 45 to 80, randomized, placebo-controlled, mean 33 months of follow-up. Funded by AbbVie and others. https://doi.org/10.1056/NEJMoa2215025
2. Bhasin S, Travison TG, Pencina KM, et al. Prostate safety events during testosterone replacement therapy in men with hypogonadism: a randomized clinical trial. JAMA Netw Open, 2023. 5,204 men, randomized (TRAVERSE). https://doi.org/10.1001/jamanetworkopen.2023.48692
3. Pencina KM, Travison TG, Cunningham GR, et al. Effect of testosterone replacement therapy on sexual function and hypogonadal symptoms in men with hypogonadism. J Clin Endocrinol Metab, 2023. 1,161 men with low libido, randomized, 2 years (TRAVERSE). https://doi.org/10.1210/clinem/dgad484
4. Bhasin S, Seidman S, Travison TG, et al. Depressive syndromes in men with hypogonadism in the TRAVERSE trial: response to testosterone-replacement therapy. J Clin Endocrinol Metab, 2024. 5,204 men, randomized. https://doi.org/10.1210/clinem/dgae026
5. Pencina KM, Travison TG, Artz AS, et al. Efficacy of testosterone replacement therapy in correcting anemia in men with hypogonadism: a randomized clinical trial. JAMA Netw Open, 2023. 5,204 men, 815 with anemia, randomized (TRAVERSE). https://doi.org/10.1001/jamanetworkopen.2023.40030
6. Snyder PJ, Bhasin S, Cunningham GR, et al. Effects of testosterone treatment in older men. N Engl J Med, 2016. 790 men aged 65+, randomized, 1 year (the Testosterone Trials). Funded by the NIH and others. https://doi.org/10.1056/NEJMoa1506119
7. Bhasin S, Brito JP, Cunningham GR, et al. Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab, 2018. https://doi.org/10.1210/jc.2018-00229
8. Snyder PJ, Bauer DC, Ellenberg SS, et al. Testosterone treatment and fractures in men with hypogonadism. N Engl J Med, 2024. 5,204 men, randomized, median 3.2 years (TRAVERSE). Funded by AbbVie and others. https://doi.org/10.1056/NEJMoa2308836
9. Cruickshank M, Hudson J, Hernández R, et al. The effects and safety of testosterone replacement therapy for men with hypogonadism: the TestES evidence synthesis and economic evaluation. Health Technol Assess, 2024. 35 randomized trials, 5,601 men. Funded by the UK National Institute for Health and Care Research. https://doi.org/10.3310/JRYT3981
10. Attia P, Schaeffer E. #310: The relationship between testosterone and prostate cancer, testosterone replacement therapy, and tools for predicting cancer aggressiveness. The Peter Attia Drive, July 22, 2024. Podcast. https://peterattiamd.com/tedschaeffer3/
11. US Food and Drug Administration. FDA issues class-wide labeling changes for testosterone products. February 28, 2025. https://www.fda.gov/drugs/drug-alerts-and-statements/fda-issues-class-wide-labeling-changes-testosterone-products
12. Seeman JI. Russell Earl Marker and the beginning of the steroidal pharmaceutical industry. Chem Rec, 2023. History. https://doi.org/10.1002/tcr.202300048
13. Tekucheva DN, Nikolayeva VM, Karpov MV, et al. Bioproduction of testosterone from phytosterol by Mycolicibacterium neoaurum strains. Bioresour Bioprocess, 2022. Lab study. https://doi.org/10.1186/s40643-022-00602-7
14. The Nobel Prize in Chemistry 1939: Adolf Butenandt and Leopold Ruzicka. NobelPrize.org. https://www.nobelprize.org/prizes/chemistry/1939/speedread/
15. Graber EG, Hosseini SMH, Wilson DM, et al. The unfolding story of protein misfolding causing Alzheimer disease in recipients of human pituitary growth hormone. J Endocr Soc, 2025. Review. https://doi.org/10.1210/jendso/bvaf029
16. Ponce OJ, Spencer-Bonilla G, Alvarez-Villalobos N, et al. The efficacy and adverse events of testosterone replacement therapy in hypogonadal men: a systematic review and meta-analysis of randomized, placebo-controlled trials. J Clin Endocrinol Metab, 2018. 4 trials, 1,779 men. https://doi.org/10.1210/jc.2018-00404
17. World Health Organization Task Force on Methods for the Regulation of Male Fertility. Contraceptive efficacy of testosterone-induced azoospermia and oligozoospermia in normal men. Fertil Steril, 1996. 399 healthy men, 15 centers in 9 countries, no comparison group. https://pubmed.ncbi.nlm.nih.gov/8654646/
18. Bhasin S, Lincoff AM, Nissen SE, et al. Effect of testosterone on progression from prediabetes to diabetes in men with hypogonadism: a substudy of the TRAVERSE randomized clinical trial. JAMA Intern Med, 2024. 1,175 men with prediabetes, randomized. https://doi.org/10.1001/jamainternmed.2023.7862