Testosterone and Heart Health: What the Evidence Actually Shows

No aspect of testosterone medicine has been more contested than its cardiovascular effects. A sequence of concerning studies in the early 2010s prompted an FDA safety review and black box warning on testosterone products. More recent large-scale trials have substantially clarified the picture.

Understanding the evidence requires separating the question of what low testosterone does to the cardiovascular system from what testosterone replacement therapy does — they are not the same question.

Low Testosterone and Cardiovascular Risk

Before asking whether TRT is safe, it is worth asking what happens to men who have low testosterone and don't treat it.

The epidemiological evidence is consistent: low testosterone is associated with increased cardiovascular risk. Large longitudinal cohort studies show that men with lower testosterone levels have higher rates of:

• Metabolic syndrome and type 2 diabetes
• Visceral adiposity
• Dyslipidemia (lower HDL, higher triglycerides)
• Atherosclerosis and coronary artery disease
• Overall cardiovascular mortality

Whether low testosterone causes cardiovascular disease or is simply a marker of underlying metabolic illness is a legitimate debate. But the association between hypogonadism and poor cardiovascular outcomes is not in doubt. [^traish2011]

This context matters when evaluating TRT risk studies: the men being treated are not starting from a cardiovascular-neutral baseline.

The Alarm Period: 2010–2014

Three publications drove substantial concern about testosterone and cardiovascular risk:

The TOM Trial (2010): A randomized trial of testosterone gel in older men with mobility limitations and high baseline cardiovascular risk was stopped early due to higher cardiovascular events in the testosterone group. [^basaria2010] The trial had notable limitations — the population was elderly with high pre-existing disease burden, and the cardiovascular event definition was broad.

Vigen et al. (2013): A retrospective study of VA patients suggested increased MI, stroke, and mortality in men prescribed testosterone. [^vigen2013] The analysis had substantial methodological criticisms, including including women in the denominator.

Finkle et al. (2014): Showed elevated non-fatal MI risk in the first 90 days after testosterone prescription, particularly in men with pre-existing coronary disease. [^finkle2014]

These studies generated significant media attention and regulatory action, but were all observational or from populations with high pre-existing disease. Confounding — men who are sicker may be more likely to receive testosterone — could not be excluded.

The TRAVERSE Trial: Current Best Evidence

The TRAVERSE trial (2023) is the most important piece of evidence in this debate. It was a randomized, double-blind, placebo-controlled trial specifically designed to assess cardiovascular safety of testosterone replacement therapy in men with hypogonadism and elevated cardiovascular risk. [^testosterone2023]

Design: 5,246 men, mean age 57, with pre-existing cardiovascular disease or elevated cardiovascular risk; testosterone levels 100–300 ng/dL; randomized to testosterone gel versus placebo; median follow-up 33 months.

Primary outcome: Major adverse cardiovascular events (MACE) — cardiovascular death, non-fatal MI, non-fatal stroke.

Results:

• MACE occurred in 7.0% of testosterone group vs. 7.3% of placebo group
• Hazard ratio 0.96 (95% CI 0.78–1.17) — non-inferior to placebo
• No significant difference in individual components (CV death, MI, stroke)

Secondary findings (increased risk in testosterone group):

• Atrial fibrillation: 3.5% vs. 2.4% (HR 1.52)
• Pulmonary embolism: 0.9% vs. 0.5% (HR 1.92)
• Acute kidney injury: 2.3% vs. 1.5% (HR 1.55)

TRAVERSE established that testosterone replacement does not increase major cardiovascular events in men with hypogonadism at elevated CV risk — the most relevant clinical population. It also identified real secondary risks (atrial fibrillation, thromboembolism) that require clinical attention.

Hematocrit and Thrombosis Risk

The most clearly established cardiovascular risk from TRT is polycythemia — elevated red blood cell mass. Testosterone stimulates erythropoiesis (red blood cell production). Hematocrit above 52–54% increases blood viscosity and venous thromboembolism risk. [^kloner2016]

This is a dose-dependent effect that requires monitoring:

• Baseline hematocrit before starting TRT
• Recheck at 3–6 months, then annually
• Dose reduction or temporary discontinuation if hematocrit exceeds 54%
• Men with pre-existing polycythemia vera or hypercoagulable states require careful assessment before TRT

The thromboembolism findings from TRAVERSE (pulmonary embolism increase) are consistent with the hematocrit mechanism.

Atrial Fibrillation

TRAVERSE found a statistically significant increase in atrial fibrillation (AFib) with testosterone. The absolute risk increase was approximately 1.1 percentage points over 33 months — small in absolute terms but real.

The mechanism is not fully established. Testosterone may affect cardiac ion channels and atrial electrophysiology. Men with pre-existing AFib or significant cardiac risk factors require this consideration in TRT decision-making.

Who Is Most at Risk

The cardiovascular risk profile of TRT is not uniform. Risk is higher in:

• Men with prior venous thromboembolism
• Men with polycythemia or hypercoagulable states
• Men with known AFib
• Men with hematocrit already in the upper normal range
• Men with severe or poorly controlled cardiovascular disease

Risk is lower in:

• Otherwise healthy men with clear symptomatic hypogonadism
• Men with low pre-treatment hematocrit
• Men without thromboembolic history

What This Means in Practice

The TRAVERSE trial effectively resolved the main question: TRT does not increase major cardiovascular events (heart attack, stroke, cardiovascular death) in appropriately screened men with hypogonadism. The earlier observational studies reflected confounding and population selection rather than a true causal cardiovascular hazard.

The residual concerns are specific and manageable:

1. Hematocrit monitoring is mandatory and dose-adjustment protocol must be followed
2. AFib risk should inform shared decision-making in men with cardiac arrhythmia history
3. Thromboembolism history requires careful assessment before TRT initiation
4. Men with TOM-trial-like profiles (elderly, high frailty, very high CV risk) may warrant more conservative management

Bottom Line

Low testosterone is independently associated with cardiovascular risk — not treating it is not a cardiovascular-neutral choice. The TRAVERSE trial established that testosterone replacement therapy does not increase major cardiovascular events in men with hypogonadism, including those with elevated baseline cardiovascular risk. Secondary risks — particularly elevated hematocrit increasing thromboembolism risk, and a modest increase in atrial fibrillation — are real and require monitoring. For appropriately selected and monitored men, TRT's cardiovascular risk profile is manageable and does not outweigh its established clinical benefits.