The largest randomized trial specifically designed to answer this question found that prescription testosterone therapy did not increase heart attacks, strokes, or other major cardiac events in men who already had cardiovascular disease or were at high risk for it. That trial, called TRAVERSE, enrolled over 5,000 men and followed them for several years, and it effectively shifted a debate that had been running for more than a decade. But the answer is not a blanket green light. Certain side effects of testosterone still carry cardiovascular implications, and the safety picture depends heavily on dose, delivery method, monitoring, and the specific heart condition involved.
Low Testosterone Is Itself a Heart Risk
One reason this question gets complicated is that having low testosterone is not a neutral state for the cardiovascular system. Multiple large studies have independently found that men with low testosterone levels face a higher risk of dying from heart disease. In one population-based study of men aged 20 to 79, those with low testosterone had roughly two and a half times the risk of dying from cardiovascular causes compared to men with higher levels, even after adjusting for smoking, physical activity, and waist circumference.1PubMed. Low serum testosterone levels are associated with increased risk of mortality in a population-based cohort of men aged 20-79 Other research has confirmed that low testosterone tracks independently with cardiovascular and all-cause mortality.2PubMed Central. Welcoming low testosterone as a cardiovascular risk factor
In men with heart failure specifically, lower testosterone correlates with worse functional status, reduced exercise capacity, and higher mortality.3PubMed. Testosterone, Hypogonadism, and Heart Failure So the question is not simply “does adding testosterone create new risk?” It is also “does leaving low testosterone untreated carry its own cardiovascular cost?” That framing matters, because a heart patient with genuinely low testosterone is not choosing between therapy and a risk-free baseline. The baseline already comes with elevated risk.
What the TRAVERSE Trial Actually Showed
For years, the evidence on testosterone therapy and heart safety was a mess of small trials and observational studies pointing in different directions. A handful of studies in the early 2010s suggested increased cardiovascular events with testosterone use, prompting the U.S. Food and Drug Administration to require new warning labels on all testosterone products in 2015.4PubMed Central. Impact of recent FDA ruling on testosterone replacement therapy (TRT) The FDA also mandated that manufacturers conduct a large cardiovascular safety trial. That trial became TRAVERSE.
TRAVERSE enrolled men aged 45 to 80 who had diagnosed low testosterone plus either established cardiovascular disease or significant risk factors for it. The study ran long enough and included enough participants to detect even moderate increases in heart attack, stroke, or cardiovascular death. The result: testosterone therapy did not increase major adverse cardiac events compared to placebo. It also did not increase prostate cancer or other prostate-related events.5PubMed Central. Long Term Cardiovascular Safety of Testosterone Therapy: A Review of the TRAVERSE Study
This was a meaningful moment. The study was not conducted in healthy young men; it was deliberately designed to test safety in exactly the population where the worry was greatest. Its findings do not prove testosterone protects the heart. They do establish that, in a monitored clinical setting with standard replacement doses, the therapy did not make heart outcomes worse.
The Coronary Plaque Finding That Complicates the Picture
Not every trial result from testosterone therapy has been reassuring. One randomized trial in older men with low testosterone used CT angiography to measure changes in coronary artery plaque over 12 months. Men receiving testosterone showed a significantly greater increase in noncalcified plaque volume compared to placebo, with an estimated difference of about 41 cubic millimeters.6PubMed Central. Testosterone Treatment and Coronary Artery Plaque Volume in Older Men With Low Testosterone
Noncalcified plaque is the type that can rupture and trigger a heart attack, so this finding raised eyebrows. However, the study was relatively small and short, and it measured an imaging marker rather than actual cardiac events. It is possible that testosterone accelerates plaque buildup in certain people without that translating into more heart attacks overall, which is roughly what TRAVERSE later suggested when it found no increase in events. Still, this result has not been fully explained, and it is one reason clinicians monitor patients carefully during treatment.
How Testosterone Affects Blood Vessels
Testosterone has direct effects on the vascular system that are generally favorable. At the blood-vessel level, its primary rapid effect is vasorelaxation, meaning it helps arteries widen. This happens through several mechanisms, including effects on potassium and calcium channels in the smooth muscle cells lining blood vessels.7PubMed. Vascular mechanisms of testosterone: The non-genomic point of view For a heart patient, relaxed arteries mean less resistance for the heart to pump against, which can reduce strain.
Testosterone also appears to improve several metabolic risk factors tied to heart disease. In men with both low testosterone and type 2 diabetes, testosterone therapy reduced insulin resistance, shrank waist circumference, and lowered total cholesterol.8PubMed. Testosterone replacement therapy improves insulin resistance, glycaemic control, visceral adiposity and hypercholesterolaemia in hypogonadal men with type 2 diabetes Each of those changes independently lowers cardiovascular risk. This helps explain why correcting genuinely low testosterone can be heart-friendly even though the hormone itself is not a cardiovascular drug.
Testosterone and Heart Failure
Heart failure is a condition where the heart cannot pump blood efficiently enough to meet the body’s needs, and patients often struggle with everyday physical tasks. Because low testosterone is common in men with heart failure and correlates with worse symptoms, researchers have tested whether replacing it helps.
The results here are genuinely mixed. An early meta-analysis pooling four small trials found that testosterone therapy improved exercise capacity by a meaningful margin, with the average increase in six-minute walk distance being about 54 meters compared to placebo.9PubMed. Testosterone supplementation in heart failure: a meta-analysis A separate trial showed similar improvements, with walking distance increasing from about 407 meters at baseline to roughly 492 meters after 12 weeks of testosterone treatment.10PubMed Central. Beneficial Effects of Testosterone Therapy on Functional Capacity, Cardiovascular Parameters, and Quality of Life in Patients with Congestive Heart Failure
However, a later and more conservative meta-analysis of randomized trials came to a different conclusion: testosterone supplementation within a physiological range was not associated with significantly improved exercise capacity, cardiac function, quality of life, or clinical outcomes in chronic heart failure patients.11PubMed Central. Testosterone Supplementation in Patients With Chronic Heart Failure: A Meta-Analysis of Randomized Controlled Trials The difference between these analyses likely reflects variation in study design, patient selection, and testosterone doses. Right now, testosterone is not a recommended treatment for heart failure itself, but the question remains open for patients who have both heart failure and confirmed low testosterone.
Blood Thickness and Clotting Risk
The most concrete and well-established cardiovascular side effect of testosterone therapy is polycythemia, a condition where the body produces too many red blood cells. Testosterone stimulates red blood cell production, which is actually useful if you are mildly anemic, but problematic if your blood gets too thick. Thicker blood flows more sluggishly and is more prone to clotting.
A study of men on testosterone therapy found that those who developed polycythemia had about a 35% higher chance of experiencing a major adverse cardiovascular event or venous blood clot in the first year of treatment compared to those who maintained normal blood-cell levels.12PubMed Central. Secondary Polycythemia in Men Receiving Testosterone Therapy Increases Risk of Major Adverse Cardiovascular Events and Venous Thromboembolism in the First Year of Therapy This is why regular blood tests to check hematocrit levels are standard practice during testosterone treatment. If levels climb too high, physicians will typically lower the dose, switch formulations, or pause therapy.
The delivery method also matters here. Injectable testosterone produces spikes in blood levels, which can drive hematocrit up more aggressively than topical gels or patches, which deliver a steadier, more gradual increase.13JAMA Internal Medicine. Comparative Safety of Testosterone Dosage Forms Heart patients who are already on blood thinners or who have a history of blood clots deserve particular attention to this risk.
Heart Rhythm and the QT Interval
Testosterone has a direct effect on the heart’s electrical system that most patients never hear about. The QT interval is a measurement on an electrocardiogram that reflects how long the heart’s lower chambers take to recharge between beats. A prolonged QT interval raises the risk of dangerous arrhythmias.
Testosterone shortens the QT interval. This is actually one reason men normally have shorter QT intervals than women. When testosterone drops, as it does during severe illness or inflammation, the QT interval can lengthen, and this has been linked to an increased risk of a particularly dangerous arrhythmia called torsades de pointes.14PubMed Central. Transient Hypogonadism Is Associated With Heart Rate-Corrected QT Prolongation and Torsades de Pointes Risk During Active Systemic Inflammation in Men
In clinical trials, testosterone replacement has been shown to counteract QT prolongation. One analysis of two randomized trials found that testosterone treatment attenuated the age-related increase in QT interval seen in placebo groups, with a reduction of about 6 milliseconds in one trial.15The Journal of Clinical Endocrinology & Metabolism. Effects of Testosterone Replacement on Electrocardiographic Parameters in Men: Findings From Two Randomized Trials A separate study in adults initiating testosterone showed significant QT shortening within just three months.16PubMed. Endocrine regulation of cardiac repolarization: early QTc shortening after testosterone in healthy AFAB adults For heart patients who take medications that can lengthen the QT interval (a surprisingly long list of drugs), this effect of testosterone could theoretically be protective, though no one prescribes testosterone for this purpose.
Prescription Therapy vs. Steroid Abuse
Any conversation about testosterone and heart safety needs to sharply separate medically supervised replacement therapy from anabolic steroid abuse. The doses involved are different by an order of magnitude. Prescription testosterone aims to restore blood levels to the normal range. Anabolic steroid users often push levels many times higher, sometimes stacking multiple compounds.
The cardiovascular consequences of abuse are severe. A large registry study following anabolic steroid users for an average of 11 years found dramatically elevated risks compared to non-users: roughly three times the risk of heart attack, about nine times the risk of cardiomyopathy (structural weakening of the heart muscle), and about three and a half times the risk of heart failure.17Circulation. Cardiovascular Disease in Anabolic Androgenic Steroid Users These numbers apply to supraphysiological doses and are not transferable to standard replacement therapy. But they do illustrate why dose and monitoring matter so much. More testosterone is emphatically not better for the heart.
What Guidelines Recommend for Heart Patients
The American Urological Association’s guideline on testosterone deficiency includes a specific recommendation for patients with recent cardiovascular events: testosterone therapy should not be started for three to six months after a heart attack, stroke, or similar event.18Journal of Urology. Evaluation and management of testosterone deficiency: AUA guideline – Section: Treatment of Testosterone Deficiency This is classified as expert opinion rather than the product of a large randomized trial, but it reflects a commonsense principle: the immediate post-event period involves acute physiological instability, and adding a hormone that affects blood viscosity, vascular tone, and cardiac electrophysiology is best deferred until things stabilize.
Beyond timing, the monitoring expectations during testosterone therapy in heart patients typically include:
- Hematocrit checks: Usually at three to six months and then annually, watching for the polycythemia risk discussed earlier.
- Lipid panels: Testosterone can shift cholesterol levels in either direction depending on the patient.
- Blood pressure: While testosterone itself did not raise blood pressure in trials of hypogonadal men with diabetes, individual responses vary.
- Symptom tracking: Leg swelling, chest pain, or shortness of breath warrant prompt evaluation in any patient on testosterone with known heart disease.
The Genetic Angle
Not everyone responds to testosterone the same way, and researchers have explored whether genetic variation in the androgen receptor might explain why some men seem more vulnerable to cardiovascular problems. The androgen receptor gene contains a repeating segment (called the CAG repeat) whose length varies between individuals, and a longer repeat is associated with a less sensitive receptor, meaning testosterone’s signal gets through more weakly.
One study in men who had experienced a heart attack found that those with longer CAG repeats had higher all-cause mortality in unadjusted analyses, though this association faded after adjusting for age.19PubMed Central. Androgen receptor polymorphism, testosterone levels, and prognosis in patients with acute myocardial infarction A separate, larger longitudinal study followed community-dwelling men for 15 years and found that CAG repeat length did not predict heart disease incidence, heart disease prevalence, or changes in HDL cholesterol and other risk factors.20PubMed. The androgen receptor gene CAG repeat polymorphism does not predict increased risk of heart disease: longitudinal results from the Massachusetts Male Ageing Study Another study found that when the androgen receptor was less sensitive (longer CAG repeats combined with lower testosterone), men on long-term testosterone therapy were more likely to develop unfavorable blood pressure and lipid profiles.21PubMed. Androgen receptor gene CAG repeat length and body mass index modulate the safety of long-term intramuscular testosterone undecanoate therapy in hypogonadal men
The practical takeaway here is limited. Genetic testing for androgen receptor sensitivity is not part of standard clinical practice before starting testosterone. But these findings do help explain why two men on the same dose can have different metabolic and cardiovascular responses, and they point toward a future where treatment might be more personalized.
Testosterone in Transgender Men
Transgender men who take testosterone as part of gender-affirming care represent another population where heart safety data is accumulating. The context differs from treating age-related hypogonadism in cisgender men: patients are often younger, have female-pattern cardiovascular risk at baseline, and take testosterone for decades.
A narrative review of recent literature, including meta-analyses and large cohort studies, concluded that it remains inconclusive whether testosterone administration increases cardiovascular event risk in transgender men, partly because long-term, high-quality studies are scarce.22PubMed Central. Cardiovascular Risk in Transgender People With Gender-Affirming Hormone Treatment A systematic review that pooled 13 observational cohort studies of transgender men on long-term testosterone found 34 cardiovascular deaths among about 7,800 individuals, corresponding to a rate of roughly 1.8 per 1,000 person-years. The certainty of evidence for long-term cardiovascular outcomes was rated low to very low.23PubMed Central. Cardiovascular mortality associated with testosterone therapy in cisgender women and transgender men: a systematic review
These numbers are difficult to interpret without a matched comparison group taking no testosterone, and the existing studies have important limitations. What can be said is that no dramatic signal of harm has appeared in the available data, but the evidence base is still immature compared to what exists for cisgender men.
Why the Evidence Took So Long to Sort Out
A review in the Canadian Journal of Cardiology summed up the state of the field before TRAVERSE: observational and randomized studies on testosterone had produced conflicting data, and meta-analyses had been inconclusive, reflecting significant differences in study design and patient populations.24PubMed Central. The Effect of Testosterone on Cardiovascular Disease and Cardiovascular Risk Factors in Men: A Review of Clinical and Preclinical Data Some of the early studies that triggered FDA warnings were observational, meaning they tracked men who happened to be prescribed testosterone and compared them to men who were not, without randomization. That makes it hard to separate the effect of the drug from the reasons doctors prescribed it in the first place, since the men receiving testosterone were often sicker to begin with.
TRAVERSE was the first trial large enough and long enough to give a reliable answer for the specific population that regulators were worried about. Even so, it has limits. It tested one formulation (a topical gel) at doses aimed at the normal range. It did not test injectable testosterone at high doses, and it did not enroll women or younger men. The question “is testosterone safe for heart patients” has been substantially answered for middle-aged and older men with low testosterone using standard replacement doses. For other populations, delivery methods, and dosing strategies, the data is thinner.
The FDA’s required warning labels remain on testosterone products despite the TRAVERSE results. Regulatory labels tend to be slow to change, and the agency has not formally revisited its 2015 position in light of the new trial data. Clinicians, meanwhile, have grown considerably more comfortable prescribing testosterone to men with cardiovascular risk factors, provided levels are genuinely low and monitoring is in place.25PubMed. Testosterone Products: Drug Safety Communication – 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