Is Testosterone Therapy Safe for Your Heart? What the Research Shows

If you are weighing testosterone therapy, the worry underneath most of the other questions is usually the same one: will this be hard on my heart? You have probably seen the old warning labels, or a headline about testosterone and heart attacks, or a brother-in-law who swears his cardiologist told him to stay away from it. That fear is reasonable, and it deserves a real answer rather than a sales pitch.

The good news is that this is one of the better-studied questions in men's health right now. A large trial designed specifically to test heart safety reported its results in 2023, and it changed the conversation. The honest news is that the same trial also flagged a few smaller signals that are worth watching. Here is what the research actually shows, where it is still uncertain, and how we handle it at NoMi Beach Health.

Where the heart worry came from

The concern was not invented out of thin air. In 2014 and 2015, the FDA required every testosterone product to carry a labeling change warning of a possible increased risk of heart attack and stroke. That step followed two observational studies that seemed to link testosterone use to more cardiovascular events (https://www.fda.gov/drugs/drug-alerts-and-statements/fda-issues-class-wide-labeling-changes-testosterone-products).

The trouble with observational studies is that they can show an association without proving cause. Men who were prescribed testosterone in those datasets were often sicker to begin with, and it is genuinely hard to separate the effect of the medication from the effect of the underlying health problems that led a man to seek treatment. The warning was a cautious call given the data available. It was never the final word, and it left a lot of men and clinicians stuck without a clear answer for the better part of a decade.

What the TRAVERSE trial changed

To settle the question properly, you need a randomized trial: take men who qualify, split them at random into a testosterone group and a placebo group, and follow both for years. That is exactly what the TRAVERSE trial did, and it published in the New England Journal of Medicine in 2023 (https://www.nejm.org/doi/full/10.1056/NEJMoa2215025).

TRAVERSE was built to be a tough test. It enrolled more than 5,000 men aged 45 to 80 who all had confirmed low testosterone plus symptoms, and who all either had established cardiovascular disease or were at high risk for it. In other words, this was not a group of healthy 30-year-olds. These were the men most likely to run into heart trouble if testosterone truly caused it.

The main finding: testosterone therapy did not raise the rate of major cardiac events. Heart attacks, strokes, and cardiovascular death happened at essentially the same rate in the testosterone group as in the placebo group. On the central question of whether testosterone strains the heart in men who genuinely need the therapy, the answer from the strongest study we have is no.

The FDA agreed the picture had changed. After the results came in, the agency removed the cardiovascular language from the boxed warning that had sat on testosterone products since the mid-2010s (https://www.fda.gov/drugs/postmarket-drug-safety-information-patients-and-providers/testosterone-information). That is a meaningful reversal, and it does not happen without solid evidence behind it.

The signals we still take seriously

A careful reading of TRAVERSE does not end at the headline. The same trial found three things that showed up more often in the testosterone group than the placebo group: atrial fibrillation, acute kidney injury, and pulmonary embolism.

The numbers are worth seeing plainly. Atrial fibrillation, an irregular heart rhythm, occurred in about 3.5% of the testosterone group versus 2.4% on placebo. Pulmonary embolism, a blood clot that travels to the lungs, occurred in about 0.9% versus 0.5% (https://www.nejm.org/doi/full/10.1056/NEJMoa2215025). These are small absolute differences, and TRAVERSE was not primarily designed to prove or disprove them. But they are not nothing, and pretending otherwise would be dishonest.

The clot signal, in particular, fits with what we already knew. Testosterone products have long carried a warning about venous blood clots, and the biology is straightforward: testosterone can raise the number of red blood cells your body makes. European experts who reviewed TRAVERSE alongside the rest of the evidence reached the same balanced conclusion -- reassuring on overall cardiovascular risk, with atrial fibrillation and clotting worth monitoring rather than dismissing (https://pmc.ncbi.nlm.nih.gov/articles/PMC12670475/).

So the fair summary is this. Testosterone therapy, used in men who actually have low testosterone, does not appear to increase your overall risk of a heart attack or stroke. It may modestly raise the odds of an irregular rhythm or a clot. Good care means capturing the benefit while keeping an eye on those specific risks.

Why hematocrit is the number we watch most

The most practical piece of heart safety on testosterone comes down to a single lab value: hematocrit. Hematocrit is the percentage of your blood made up of red blood cells. Testosterone tends to push it up, and when blood gets too thick, it flows less easily and clot risk rises. That is the likely mechanism behind the clotting signal in the research.

This is measurable and manageable, which is what makes it so important. FDA labeling is explicit: if hematocrit climbs above 54%, the dose should be lowered or the therapy paused until it comes back down (https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/021454s036lbl.pdf). Analyses of men on testosterone suggest that those who develop a high red-cell count carry more clot and cardiovascular risk, especially in the first year, which is exactly when close monitoring pays off most (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9881804/).

A rising hematocrit is not a reason to fear testosterone. It is a reason to have someone checking your blood on a schedule and willing to adjust the dose. Caught early, it is a simple fix. Ignored for a year, it becomes the kind of problem that lands in the small print of a trial's adverse-event table.

Who should be more cautious

The heart data is reassuring for most men, but not every man starts from the same place. A few histories call for a slower, more careful approach:

• A prior blood clot in the leg or lungs, or a known clotting disorder
• A history of atrial fibrillation or another significant arrhythmia
• Heart failure that is not well controlled
• A hematocrit that is already high before you start
• Untreated sleep apnea, which can push red-cell counts up on its own

None of these is an automatic no. What they change is the conversation and the monitoring. A man with well-controlled atrial fibrillation and true, symptomatic deficiency can often still be a reasonable candidate, but he deserves a frank talk about the tradeoff and a plan for watching his rhythm and his labs. This is also why guidelines insist on confirming genuinely low testosterone on two morning blood draws before anyone writes a prescription (https://www.auanet.org/guidelines-and-quality/guidelines/testosterone-deficiency-guideline). The safety evidence applies to men who actually have a deficiency. It does not extend to pushing an already-normal level higher.

How we monitor patients at NBH

At NoMi Beach Health, Dr. Jezwah Harris structures testosterone therapy around confirmed diagnosis and steady follow-up, not a fast intake and an easy refill. Before starting, that means two morning testosterone levels, a baseline hematocrit, a blood pressure and cardiovascular history, and an honest look at your personal risk factors from the list above.

Once you are on therapy, we recheck hematocrit and review blood pressure and any new symptoms around six to twelve weeks after starting or changing a dose, then at least once or twice a year after that. If your hematocrit drifts up, we lower the dose or pause rather than wait. We aim for a physiologic range rather than an aggressive ceiling, because there is no heart-safety benefit to running high and there is a real downside. And if you have heart disease or an arrhythmia, we coordinate with your cardiologist instead of working around them.

The evidence supports testosterone therapy for men who need it, including men with heart risk. It also asks for attention. Those two things are not in conflict -- they are the whole point of doing this well.

If you have been putting off testosterone therapy because you were not sure it was safe for your heart, or you are already on it through a clinic that has stopped checking your labs, our men's health services page explains what a more careful approach looks like. You can also call us at (786) 744-5152 to talk through your own history and whether your current plan is set up to protect you. For more on how we think about men's health, our blog covers the broader picture.