Why TRT Safety Was Questioned
Between 2010 and 2014, several observational studies raised alarms about a potential link between TRT and cardiovascular events — heart attacks, strokes, and cardiovascular death. These studies had significant methodological limitations (retrospective design, confounding variables, inconsistent populations), but the signal was enough to trigger regulatory action.
In 2015, the FDA mandated a class-wide black-box warning on all testosterone products, alerting prescribers and patients to potential cardiovascular risks. This warning shaped the TRT conversation for nearly a decade, making many men hesitant to start therapy and many primary care physicians reluctant to prescribe it.
The FDA simultaneously required manufacturers to fund a definitive, prospective clinical trial to settle the question. That trial was TRAVERSE.
The TRAVERSE Trial: Study Design
TRAVERSE (Testosterone Replacement Therapy for Assessment of Long-term Vascular Events and Efficacy Response in Hypogonadal Men) was published in the New England Journal of Medicine in 2023. It was specifically designed to provide the kind of evidence the observational studies couldn't.
The design: Randomized, double-blind, placebo-controlled. This is the gold standard of clinical evidence — the same level of rigor used to evaluate new pharmaceuticals for FDA approval.
The population: 5,246 men aged 45 to 80 with documented hypogonadism (total testosterone below 300 ng/dL on two morning draws) AND pre-existing cardiovascular disease or high cardiovascular risk. This was not a low-risk population — it was deliberately chosen to test TRT in the men most likely to experience cardiovascular harm if such harm existed.
The follow-up: Mean follow-up of 22 to 33 months. This provided enough time to capture both acute and medium-term cardiovascular events.
The intervention: Testosterone gel (1.62%) applied daily, titrated to achieve serum levels of 350–750 ng/dL, versus matching placebo gel.
Key Findings
The primary endpoint — Major Adverse Cardiovascular Events (MACE):
Cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke occurred in 7.0% of the testosterone group versus 7.3% of the placebo group. TRT met the statistical threshold for non-inferiority. In plain English: testosterone therapy did not increase the rate of heart attacks, strokes, or cardiovascular death compared to placebo, even in high-risk men.
Prostate cancer:
TRAVERSE also provided definitive evidence that testosterone therapy does not increase the risk of developing prostate cancer or high-grade prostatic disease. This finding removed another long-standing concern that had been used to discourage TRT.
Secondary findings requiring monitoring:
While the major cardiovascular safety signal was clearly resolved, TRAVERSE did identify smaller signals that informed updated monitoring guidelines:
| Finding | Testosterone Group | Placebo Group | Clinical Significance |
|---|---|---|---|
| Systolic blood pressure change | +0.3 mmHg | -1.5 mmHg | Minimal but statistically significant |
| Nonfatal arrhythmias | 5.2% | 3.3% | Monitoring recommended |
| Atrial fibrillation | 3.5% | 2.4% | Monitoring recommended |
| Acute kidney injury | 2.3% | 1.5% | Monitoring recommended |
These secondary findings are clinically relevant but represent modest absolute risk differences. They support the case for ongoing monitoring rather than avoidance of therapy.
The 2025 FDA Label Changes
Based on TRAVERSE data, the FDA executed a class-wide labeling update for all testosterone products in February 2025. The changes were significant:
Removed: The restrictive cardiovascular risk language from the black-box warning that had been in place since 2015. The unsupported prostate cancer warning was also removed.
Added: New guidance recommending blood pressure monitoring for patients on TRT, based on the small but measurable BP signal in the TRAVERSE data. Updated language regarding the importance of monitoring hematocrit and the secondary arrhythmia findings.
This label change represented a major shift in the regulatory posture toward TRT. For practitioners who had been cautious about prescribing based on the old warnings, the updated labeling provides clearer clinical guidance grounded in rigorous prospective data.
What You Should Still Monitor
TRT being cardiovascular-safe as a class doesn't mean it requires no monitoring. Every therapy has parameters that need management. For TRT, the key monitoring targets are:
Hematocrit: The most clinically significant ongoing safety concern. Must remain below 52%. Check at baseline, 6–12 weeks after starting, and every 6 months ongoing.
Blood pressure: The TRAVERSE data supports checking BP at follow-up visits. A 1–2 mmHg change is clinically minimal, but worth tracking in men with pre-existing hypertension.
Estradiol: Not a safety concern from TRAVERSE specifically, but essential for symptom management and quality of life on TRT.
PSA: While TRAVERSE showed no increased prostate cancer risk, baseline and periodic PSA monitoring remains standard practice to catch any pre-existing prostate pathology that might be stimulated by androgens.
For a complete breakdown of every monitoring biomarker, see our bloodwork interpretation guide.
The Bottom Line on Safety
Key Takeaway: The TRAVERSE trial — the largest and most rigorous cardiovascular safety study of TRT ever conducted — found no increased risk of heart attacks, strokes, or cardiovascular death in hypogonadal men, even those with pre-existing heart disease. The FDA removed its cardiovascular warning in response. TRT is a safe therapy when properly monitored. The emphasis is on "properly monitored."
Safe TRT requires a competent provider who monitors your hematocrit, manages your estradiol, checks your blood pressure, and adjusts your protocol based on data. The therapy itself isn't the risk factor — inadequate oversight is.
If you're considering TRT and safety was your primary hesitation, the evidence is clear. The more relevant question is: which provider will give you the level of monitoring that keeps the therapy safe? Our clinic comparison evaluates providers on exactly that criteria.