For men with clinically low testosterone (below 300 ng/dL), taking prescribed testosterone replacement therapy is generally safe, though it carries specific risks that require regular blood monitoring. The largest cardiovascular safety trial to date found that testosterone therapy was no worse than placebo for heart attacks and strokes, even in men who already had heart disease. That said, “safe” depends heavily on whether you actually need it, how it’s administered, and whether you and your doctor are tracking the right numbers.
What the Biggest Safety Trial Found
For years, the main concern with testosterone therapy was heart risk. The TRAVERSE trial, the largest and longest study designed specifically to answer this question, enrolled men with low testosterone who either had existing cardiovascular disease or were at high risk for it. The result: testosterone was noninferior to placebo for major cardiac events like heart attack, stroke, and cardiovascular death. Put simply, men taking testosterone didn’t have more heart problems than men taking a placebo.
The study also looked at whether the blood-thickening effect of testosterone (more on that below) translated into dangerous clots. It didn’t. The hazard ratio for venous blood clots was 0.94, meaning there was no meaningful increase in clot risk tied to changes in blood thickness during the trial.
Blood Thickness Is the Most Common Risk
Testosterone stimulates your bone marrow to produce more red blood cells. This is a well-known, dose-dependent effect, and it’s the reason regular blood work is non-negotiable during therapy. The key number your doctor watches is your hematocrit, a measure of how much of your blood volume is made up of red blood cells.
The U.S. Department of Veterans Affairs clinical guidelines set clear thresholds: if your hematocrit rises above 51%, your dose needs to be reduced. If it crosses 54%, testosterone should be stopped entirely. Blood that’s too thick increases the risk of clots, stroke, and other circulatory problems. This is why hematocrit is checked at baseline, again at three to six months, and then annually for as long as you’re on therapy.
Prostate Cancer Concerns Are Largely Outdated
The idea that testosterone fuels prostate cancer dates back to the 1940s, but modern evidence doesn’t support it. According to Mayo Clinic, current data shows no link between testosterone replacement therapy and the development of new prostate cancer. Men on testosterone in clinical studies did not have higher rates of prostate cancer than men who weren’t taking it.
What can happen is that PSA levels (a protein marker sometimes associated with prostate issues) rise after starting testosterone. Higher PSA leads to more biopsies, which leads to more detection of cancers that might have gone unnoticed otherwise. This is a screening effect, not a causal one. Still, men between 40 and 69, especially those at higher risk, are typically advised to get a PSA check and digital rectal exam within the first three to twelve months of starting therapy.
Liver Safety Depends on the Formulation
Older oral testosterone pills, first developed in the 1930s, were chemically modified in a way that forced the drug through the liver and caused real damage: abnormal liver function tests, bile flow problems, and jaundice. Those formulations gave oral testosterone a bad reputation that lingered for decades.
Newer oral formulations work differently. They’re absorbed through the intestinal lymphatic system, bypassing the liver almost entirely before entering the bloodstream. The first FDA-approved version of this type, approved in 2019, showed no clinically significant liver toxicity in phase 3 trials involving hundreds of patients. In head-to-head comparisons with topical gels, liver function tests were essentially the same between groups. If you’re using injections, gels, or patches, liver toxicity isn’t a meaningful concern at all, since those routes skip the digestive system entirely.
Sleep Apnea Can Get Worse
Testosterone therapy can worsen obstructive sleep apnea, and this risk is often underappreciated. Several studies have documented increases in the severity of breathing interruptions during sleep, along with drops in blood oxygen levels, in men taking testosterone.
The mechanisms are complex. Testosterone may alter the function of the muscles that keep your airway open during sleep, change how your brain responds to drops in oxygen and rises in carbon dioxide, and increase your body’s overall oxygen demand. If you already snore heavily, wake up gasping, or have been told you stop breathing in your sleep, this is worth discussing before starting therapy. Untreated or unmonitored sleep apnea raises its own cardiovascular risks, which could offset the relative cardiac safety seen in clinical trials.
Fertility Is Significantly Affected
This is one of the most important safety considerations for younger men, and one that’s frequently overlooked. Taking testosterone shuts down your body’s own production of the hormones that drive sperm creation. Sperm counts typically drop below 1 million per milliliter (far below the normal range of 15 million or more) within about three and a half months of starting therapy. Many men become completely infertile while on testosterone.
The good news is that fertility usually returns after stopping. Data from contraception research shows that about 67% of men recover adequate sperm production within 6 months of stopping testosterone, 90% by 12 months, and virtually all by 24 months. However, recovery can sometimes take years, and in rare cases the damage may be permanent. If you’re planning to have children, testosterone therapy in its standard form is not the right choice. There are alternative treatments that raise testosterone while preserving fertility.
Mood Effects at Therapeutic Doses
The “roid rage” stereotype comes from supraphysiological doses used in bodybuilding, not from prescribed therapy. At therapeutic doses designed to bring levels into the normal range (roughly 400 to 700 ng/dL), most men report improved mood, energy, and motivation. That said, limited clinical data does link abnormally high testosterone levels to increased rates of both depressive symptoms and hypomanic episodes (periods of elevated mood, impulsivity, and reduced need for sleep). This is one reason doctors aim to keep your levels within a normal range rather than pushing them as high as possible.
Gels, Injections, and Patches Differ
The delivery method you choose affects both your daily experience and your risk profile. Injections (typically given every one to two weeks) create peaks and troughs in testosterone levels. You may feel great in the days after an injection and sluggish as the next one approaches. The target is a serum level between 400 and 700 ng/dL measured about one week after your most recent shot.
Topical gels provide steadier day-to-day levels but come with a transfer risk: testosterone can rub off on partners, children, or pets through skin contact. This is a genuine safety concern, particularly for women and children, who can develop symptoms of excess testosterone from repeated exposure. Gels also convert more testosterone into a potent related hormone called DHT (about a fivefold increase versus roughly twofold with injections), though the long-term clinical significance of that difference isn’t fully established. Patches can cause skin irritation at the application site. Injections can cause pain or minor bleeding and aren’t ideal for men on blood thinners.
What Monitoring Looks Like
Safe testosterone use requires a structured monitoring schedule, especially in the first year. Your testosterone level itself should be checked at three to six months to confirm the dose is working and you’re in the target range. Hematocrit follows the same timeline: baseline, three to six months, then annually. Prostate screening (PSA and a physical exam) is recommended within the first year for men in the appropriate age and risk categories, then according to standard cancer screening guidelines. If your total testosterone level exceeds 900 ng/dL, your dose should be reduced regardless of how you feel, since levels that high increase the likelihood of side effects without additional benefit.
The bottom line is that testosterone therapy, when prescribed for a genuine deficiency and monitored properly, has a well-characterized safety profile. The risks are real but manageable. The biggest dangers come from skipping blood work, ignoring symptoms like heavy snoring or swollen legs, or using testosterone without a confirmed diagnosis of low levels.