Is Testosterone Replacement Therapy Safe? What the Evidence Shows

Why this question exists

In 2015 the FDA required a warning on testosterone products about possible cardiovascular risk. That warning was based on a small number of observational studies with real methodological problems, and it shaped a decade of conversations in exam rooms.

Men still bring it up almost every week. It's a fair question, and the answer has changed.

What the largest trial actually found

TRAVERSE was the randomized trial the FDA asked for. It enrolled more than 5,200 men aged 45 to 80 with symptomatic low testosterone and either existing cardiovascular disease or high risk for it — the exact population people worried about.

Men were randomized to testosterone gel or placebo and followed for a median of about two years. Major adverse cardiac events — cardiovascular death, heart attack, stroke — were not higher in the testosterone group.

In 2025 the FDA updated testosterone labeling to reflect this, removing the boxed cardiovascular language while keeping warnings about blood pressure.

That is meaningful. It is also not the same as "testosterone is good for your heart." The trial showed non-inferiority for cardiac events. It did not show benefit.

The risks that are real

TRAVERSE and the trials before it did flag things worth watching:

• Higher hematocrit. Testosterone stimulates red blood cell production. Too thick is a genuine problem, and it's the most common reason I adjust or pause a dose.
• Atrial fibrillation and pulmonary embolism occurred slightly more often in the testosterone group.
• Sleep apnea can worsen, particularly in men who already snore heavily or have untreated apnea.
• Acne, oily skin, and fluid retention, usually dose-related.
• Fertility suppression. This one matters most to men in their 30s and 40s. Testosterone shuts down the body's own signal to the testes and sperm production drops, sometimes substantially.
• Estradiol conversion, which can cause breast tenderness or moodiness when it runs high.

Prostate cancer is the fear most men name first. The current evidence does not show that replacement-dose testosterone causes prostate cancer, but it can accelerate a cancer that already exists, which is why PSA screening before and during treatment matters for men in the appropriate age range.

The distinction that changes the answer

There's a difference between replacing testosterone in a man who is genuinely deficient and pushing levels above the normal range because higher sounds better.

Almost everything reassuring in the literature comes from replacement dosing — bringing a low level into the mid-normal range and keeping it there. The risk profile of high-dose or unmonitored testosterone, including what men buy online or from a gym source, is not the same thing and should not be compared.

What makes it safe in practice

Not the prescription. The follow-up.

For men I treat, that means confirming low testosterone on two separate morning blood draws before starting, checking hematocrit and estradiol early and then periodically, running PSA when age-appropriate, watching blood pressure, and asking directly about sleep and fertility plans before we begin.

If hematocrit climbs, we lower the dose or change the interval. If symptoms don't improve after an adequate trial at a good level, testosterone probably wasn't the whole answer and we look elsewhere.

Who probably shouldn't start

Men with untreated severe sleep apnea, an unexplained high hematocrit, active prostate or breast cancer, uncontrolled heart failure, a recent cardiac event, or plans to conceive in the near term. Those are conversations, not permanent no's, but they change the plan.

The bottom line

Testosterone replacement is reasonably safe when it's prescribed for a diagnosed deficiency, dosed to a normal range, and monitored on a schedule.

It is not a longevity drug, it is not appropriate for every tired man over 40, and it is not something to run without labs. The safety comes from the structure around it.