Testosterone Therapy and Your Heart: What the Latest Evidence Actually Says

Testosterone therapy is one of the most asked-about topics in my office. Men in their forties, fifties, sixties, and beyond come in carrying a lab result, a billboard, a podcast clip, or a friend's recommendation, and they want to know whether starting testosterone is going to help their energy and mood without quietly damaging their heart. The honest answer used to be uncertain. The honest answer in 2026 is much clearer than it was even three years ago, and I want to walk you through what changed.

I'm Dr. Damian Rasch, a cardiologist in Encinitas. This article is meant for the patient or partner trying to make sense of the headlines. It is not a substitute for a one-on-one evaluation with a physician who can review your labs and your full history. With that said, here's what we now know.

The Question, in Plain Terms

When a man's body makes too little testosterone, the medical word for that is hypogonadism. The symptoms include low libido, fatigue, mood changes, loss of muscle, increased body fat, erectile dysfunction, and sometimes hot flashes or a drop in bone density. Testosterone replacement therapy (TRT) treats those symptoms by adding back the hormone the body isn't producing in adequate amounts.

Around 2013 and 2014, two observational studies suggested that men on TRT might have higher rates of heart attack and stroke. The FDA responded in 2015 with a safety warning. For nearly a decade, cardiologists and primary care physicians had to weigh the symptom benefits of TRT against an unsettled cardiovascular risk picture. That changed in 2023 with the publication of a large randomized trial called TRAVERSE.

What Caused the Original Concern

Two studies in particular drove the cardiovascular alarm.

The first was a 2013 paper in JAMA by Vigen and colleagues, looking at over 8,700 men in the Veterans Affairs system who had undergone coronary angiography and had low testosterone. Men who started TRT seemed to have a higher rate of death, heart attack, and stroke than men who didn't. The study was retrospective, the populations weren't well matched, and absolute event rates were close, but the headline was alarming.

The second was a 2014 paper by Finkle and colleagues in PLOS ONE, looking at over 55,000 men in an insurance database. The authors reported a roughly doubled risk of heart attack in the 90 days after starting TRT, mostly in older men or those with prior heart disease.

Both papers had methodological limits. They were observational, meaning they couldn't prove cause and effect. Men who started TRT may have been sicker, more symptomatic, or different in ways the data couldn't capture. Still, the FDA decided the signal was strong enough to act on. The 2015 boxed warning followed.

TRAVERSE: The Trial That Changed the Conversation

The TRAVERSE trial, published in the New England Journal of Medicine in 2023 by Lincoff and colleagues, was the randomized study cardiologists had been waiting for. It enrolled 5,246 men aged 45 to 80 who had symptomatic hypogonadism with two morning testosterone readings under 300 ng/dL and either established cardiovascular disease or a high cardiovascular risk profile. Men were randomly assigned to a transdermal testosterone gel or to a matching placebo. The median follow-up was about 33 months.

The primary endpoint was a composite of cardiovascular death, nonfatal heart attack, and nonfatal stroke. The result: 7.0 percent of men in the testosterone group reached the endpoint, compared with 7.3 percent in the placebo group. The hazard ratio was 0.96 with a confidence interval that easily met the prespecified threshold for noninferiority. In plain English, TRT in this population did not increase the risk of major adverse cardiovascular events.

That single finding changed practice. The 2015 boxed warning was relaxed in 2024-2025, with the FDA acknowledging that TRT does not appear to raise the risk of major heart attacks or strokes in men with confirmed hypogonadism.

What TRAVERSE Did Not Make Disappear

A noninferior result on MACE is not the same as a clean bill of health. TRAVERSE also reported several secondary findings that I share with every patient considering TRT.

Atrial fibrillation occurred in 3.5 percent of the testosterone group versus 2.4 percent of placebo. AFib isn't trivial. It's a leading cause of stroke when untreated, and it changes how we think about anticoagulation. If you have a personal or family history of AFib or sleep apnea, this matters to your decision.

Pulmonary embolism occurred in 0.9 percent versus 0.5 percent. This was a smaller absolute difference but consistent with prior signals around blood clots and TRT. The FDA had already added a clot warning in 2014, and that warning still stands.

Acute kidney injury was modestly more common in the TRT group (2.3 percent versus 1.5 percent).

Prostate cancer rates were similar between groups (0.5 percent versus 0.3 percent), which was reassuring. Long-standing concerns that TRT might fuel prostate cancer growth were not confirmed in this trial, though we still don't start TRT in men with active or untreated prostate cancer.

So the modern summary is this: TRT is reasonably safe from a heart attack and stroke perspective when used in men with confirmed hypogonadism. It carries real concerns around AFib, blood clots, and erythrocytosis (the thickening of the blood that I'll cover next), and those concerns shape monitoring.

Erythrocytosis: The Number You'll Get Tired of Hearing About

Testosterone increases red blood cell production. That's a normal physiologic effect of the hormone. In a healthy young man, it's part of why testosterone supports muscle and oxygen carrying. In a man on TRT, it can push the hematocrit (the percentage of your blood that is red cells) into territory that increases blood viscosity and clotting risk.

The threshold most clinicians use is a hematocrit above 54 percent. At that point we either lower the dose, hold the medication, or send the patient for therapeutic phlebotomy (a blood donation done for medical reasons rather than for someone else). Intramuscular testosterone tends to raise hematocrit more than transdermal gel, partly because peak levels are higher.

If your TRT is working but your hematocrit climbs, the answer is rarely to abandon TRT. The answer is usually to adjust the dose, switch the formulation, or schedule periodic phlebotomy. This is one of the standing reasons we monitor labs every few months early on and at least yearly afterward.

Who Actually Has Hypogonadism

Not every man with low energy or low libido has hypogonadism. The 2018 Endocrine Society guideline, written by a panel led by Dr. Bhasin, lays out a specific path to diagnosis.

First, a man needs symptoms consistent with hypogonadism. Then he needs two morning blood draws (testosterone is highest in the morning) showing total testosterone below 300 ng/dL. One low value doesn't make a diagnosis. Levels move with sleep, illness, stress, and time of day.

If the picture is unclear (for instance, in obese men whose sex hormone-binding globulin is low and total testosterone underestimates the active hormone), we measure free testosterone or calculated free testosterone. We also check LH and FSH to figure out whether the testes are the problem (primary hypogonadism) or whether the signal from the brain is the problem (secondary hypogonadism). If secondary hypogonadism is suggested, we check prolactin, iron studies, and sometimes get an MRI of the pituitary.

This workup matters. It's the gate that prevents TRT from being used for symptoms that have a different explanation, including depression, sleep apnea, untreated diabetes, or thyroid disease. Each of those has its own treatment, and TRT won't fix any of them.

When TRT Should Not Be Started

Both the Endocrine Society and the AUA list a set of contraindications and cautions. The clearest contraindications are active or untreated prostate cancer, an unevaluated prostate nodule, an unexplained PSA above 4 (or above 3 in higher-risk men), male breast cancer, hematocrit above 48 percent at baseline, untreated severe sleep apnea, severe lower urinary tract symptoms, uncontrolled heart failure, recent heart attack or stroke (within the past three to six months), and a desire for fertility.

That last one surprises many men. TRT suppresses the brain's signal to the testes, which suppresses the body's own testosterone production and, more relevant for fertility, suppresses sperm production. Many men become functionally infertile on TRT, sometimes permanently. If having biological children is on your timeline, we have to talk through alternatives such as clomiphene or human chorionic gonadotropin (hCG) before you start TRT.

Monitoring: The Long Game

Once a man starts TRT, we don't just send him home with a prescription. The standard monitoring schedule looks something like this:

At three to six months: total testosterone (timed appropriately for the formulation), hematocrit, PSA, and a check-in on symptoms.

At twelve months: the same labs plus a digital rectal exam if appropriate based on age and risk.

Annually thereafter: testosterone, hematocrit, PSA, blood pressure, and a symptom review. Bone density studies are sometimes added.

If you develop new palpitations or an irregular pulse on TRT, mention it. AFib can be silent, and given the trial signal, we have a low threshold to check an EKG or get a heart monitor in TRT patients with new rhythm symptoms.

TRT Is Not a Lifestyle Choice

A point I make in clinic regularly: TRT is treatment for a defined medical condition. It is not anti-aging, it is not muscle enhancement for healthy men with normal levels, and it is not a substitute for sleep, exercise, weight management, and stress reduction. Many men come to me convinced their fatigue must be testosterone, when in fact the cause is poor sleep, undiagnosed sleep apnea, alcohol use, depression, or lifestyle.

If a workup shows clear hypogonadism with symptoms, TRT is reasonable, and the modern evidence supports its cardiovascular safety in carefully selected men. If a workup shows borderline numbers and ambiguous symptoms, the right move is often to address sleep, weight, exercise, and mental health first and recheck the labs in three to six months.

There's also a growing market for testosterone prescribed online without a thorough evaluation. I won't name names, but anyone can find these clinics in five minutes. The product is the same testosterone available through your physician. The difference is in the workup, the monitoring, and the safety net. If you go that route, please at least share the prescription with your primary care doctor and your cardiologist so we can monitor labs and catch problems early.

Special Situations

After a heart attack or stroke

Most guidelines recommend waiting three to six months after a major cardiovascular event before initiating TRT. The reason is partly the natural variability in testosterone after illness, and partly the desire to allow the patient to stabilize on their cardiovascular medications and lifestyle plan first.

Men with sleep apnea

TRT can worsen obstructive sleep apnea. If you have sleep apnea, we'd prefer it be diagnosed and treated (usually with CPAP) before starting TRT. If you've never been tested and you snore, are sleepy during the day, or have a partner who reports breathing pauses overnight, get a sleep study before TRT.

Men with atrial fibrillation

If you already have AFib, the modest increased AFib risk from TRT is something to factor in. We weigh the symptom benefits, the alternatives, and your stroke risk score (CHA2DS2-VASc). For some men with controlled AFib, TRT is still reasonable. For others with paroxysmal AFib that has been hard to control, we may suggest other strategies first.

Men with severe heart failure

TRT can cause fluid retention. In stable heart failure, this is usually manageable. In poorly controlled heart failure, it adds another variable. We coordinate with the patient's heart failure team before starting.

Men on anticoagulants

TRT does not directly interact with most anticoagulants, but the combined risk picture (clotting versus bleeding) deserves a thoughtful conversation, especially given the modest VTE signal in TRAVERSE.

A Word About Trial Generalizability

TRAVERSE was a remarkable trial, but it studied a specific population: men 45 to 80 with documented hypogonadism and either established cardiovascular disease or high cardiovascular risk. The reassurance about MACE applies most strongly to that population. Younger men without cardiovascular disease, men with very low baseline testosterone, men on intramuscular formulations rather than transdermal, and men who use TRT outside guideline-recommended doses, were not the trial population. We extrapolate carefully from TRAVERSE to those situations rather than assuming identical safety profiles.

For the bulk of patients I see, the TRAVERSE result is genuine reassurance. That does not mean TRT is risk-free. The list of monitoring items, the AFib signal, the erythrocytosis risk, the clotting concern, the prostate considerations, and the fertility impact are all still real.

Common Patient Questions

If my testosterone is low and I have no symptoms, should I treat it?

No. Both the Endocrine Society and AUA guidelines require both a low level and consistent symptoms before starting TRT. A number in isolation doesn't make a diagnosis.

Will TRT improve my erectile function?

Sometimes. If hypogonadism is the cause of the ED, TRT often helps. If the cause is vascular, neurologic, psychological, or medication-related, TRT alone is unlikely to fix it. ED has many causes, and a workup matters.

Is gel or injection better?

Each has trade-offs. Gel gives steadier daily levels and lower peak hematocrit, with a small risk of skin transfer to family members. Injections give peaks and troughs in mood and energy, raise hematocrit more, and require less day-to-day attention. Pellets last months but require a minor implant procedure. Patches are an option for some. We pick based on patient preference, lifestyle, and lab response.

How fast will I notice a difference?

Sexual symptoms often improve within three to six weeks. Mood and energy follow over six to twelve weeks. Body composition changes (muscle, fat) take three to six months and require exercise to be meaningful. Bone density changes take a year or more.

Will I have to take TRT forever?

Most men with documented primary hypogonadism do remain on TRT long-term. Men with secondary hypogonadism from a reversible cause (such as opioid use, severe stress, or untreated sleep apnea) may regain natural production after the underlying issue is addressed. Stopping TRT abruptly drops levels back to baseline within weeks, and symptoms typically return.

Does TRT cause prostate cancer?

The modern data, including TRAVERSE, do not support a meaningful increase in prostate cancer with TRT in men without prior prostate cancer. We still don't initiate TRT in men with active or recent prostate cancer, and we monitor PSA on therapy. The old fear that TRT lights a fire under the prostate has softened with better evidence.

What if I just want more energy and muscle?

If your testosterone is normal, TRT is not the right tool. The risks (clotting, AFib, hematocrit, infertility) accumulate without offsetting benefit when there's no deficiency to correct. Sleep, strength training, protein intake, and dealing with depression or sleep apnea are far better starting points for healthy men.

Putting It Together

If you've made it this far, here's the short version of how I think about testosterone therapy in 2026:

A man with bothersome symptoms and confirmed low morning testosterone, after a workup that has ruled out other causes and any contraindications, is a reasonable candidate for TRT. The cardiovascular safety picture, after TRAVERSE, is much more favorable than the FDA's 2015 warning suggested. The AFib, clot, hematocrit, and prostate considerations are real but manageable with appropriate monitoring. TRT is treatment for hypogonadism, not anti-aging, and shouldn't be started without an evaluation.

If you're considering TRT, I'd encourage you to find a physician who will spend the time on the workup and the long-term monitoring. The decision deserves more than a five-minute online questionnaire. Whether I'm that physician for you or your prescriber is someone else, please make sure your cardiologist is in the loop. The evidence is clearer now than it was a decade ago, and that should make the conversation calmer, not noisier.

References

1. Lincoff, A. Michael, Shalender Bhasin, Panagiotis Flevaris, et al. "Cardiovascular Safety of Testosterone-Replacement Therapy." New England Journal of Medicine 389, no. 2 (2023): 107-117.

2. Bhasin, Shalender, Juan P. Brito, Glenn R. Cunningham, et al. "Testosterone Therapy in Men with Hypogonadism: An Endocrine Society Clinical Practice Guideline." Journal of Clinical Endocrinology and Metabolism 103, no. 5 (2018): 1715-1744.

3. Mulhall, John P., Landon W. Trost, Robert E. Brannigan, et al. "Evaluation and Management of Testosterone Deficiency: AUA Guideline." Journal of Urology 200, no. 2 (2018): 423-432.

4. Vigen, Rebecca, Colin I. O'Donnell, Anne E. Barón, et al. "Association of Testosterone Therapy With Mortality, Myocardial Infarction, and Stroke in Men With Low Testosterone Levels." JAMA 310, no. 17 (2013): 1829-1836.

5. Finkle, William D., Sander Greenland, Gregory K. Ridgeway, et al. "Increased Risk of Non-Fatal Myocardial Infarction Following Testosterone Therapy Prescription in Men." PLOS ONE 9, no. 1 (2014): e85805.

6. Heidelbaugh, Joel J., and Anatoly Belakovskiy. "Testosterone Replacement Therapy for Male Hypogonadism." American Family Physician 109, no. 5 (2024): 449-456.

7. U.S. Food and Drug Administration. "FDA Cautions About Using Testosterone Products for Low Testosterone Due to Aging; Requires Labeling Change to Inform of Possible Increased Risk of Heart Attack and Stroke With Use." FDA Drug Safety Communication, March 3, 2015.

8. U.S. Food and Drug Administration. "FDA Updates Labeling for Testosterone Products Following TRAVERSE Trial Results." FDA Drug Safety Communication, 2025.

9. Snyder, Peter J., Susan S. Ellenberg, Glenn R. Cunningham, et al. "The Testosterone Trials: Seven Coordinated Trials of Testosterone Treatment in Elderly Men." Clinical Trials 11, no. 3 (2014): 362-375.

10. Corona, Giovanni, Andrea Sansone, Francesco Pallotti, et al. "Endogenous Testosterone Levels and Cardiovascular Risk: Meta-Analysis of Observational Studies." Journal of Sexual Medicine 18, no. 7 (2021): 1098-1112.

Published on damianrasch.com. The above information was composed by Dr. Damian Rasch, drawing on individual insight and bolstered by digital research and writing assistance. The information is for educational purposes only and does not constitute medical advice.