Testosterone therapy is generally safe when prescribed for a confirmed deficiency and monitored with regular blood work, but it carries real risks that depend on your health history, the delivery method you use, and how closely you and your doctor track key markers. A meta-analysis of 30 randomized trials involving over 11,500 patients found no significant increase in heart attacks, strokes, or death in men using testosterone compared to placebo. That’s reassuring, but it doesn’t mean the treatment is risk-free for everyone.
Heart and Stroke Risk
Cardiovascular safety has been the biggest concern around testosterone therapy for years. The pooled data from 30 clinical trials shows that rates of heart attack, stroke, and cardiovascular death were statistically comparable between men taking testosterone and men taking a placebo. That said, testosterone is not considered safe for anyone who has had a heart attack, stroke, or a cardiac procedure within the last four months. Men with poorly controlled heart failure are also advised against it, because testosterone can cause fluid retention that worsens swelling and strain on the heart.
How you take testosterone also matters. Research from UNC’s Gillings School of Global Public Health found that injections carry a higher short-term risk of cardiovascular events, stroke, hospitalization, and death compared to gels or patches. Injections create spikes of abnormally high testosterone that then drop off before the next dose. Gels and patches deliver a steadier, more moderate increase, and their risk profiles are similar to each other and lower than injections.
Blood Thickening: The Most Common Safety Issue
Testosterone stimulates your bone marrow to produce more red blood cells. In moderation, that’s fine. But if red blood cell concentration climbs too high, a condition called erythrocytosis, your blood becomes thicker and harder to pump, raising the risk of clots, stroke, and pulmonary embolism. The widely accepted safety ceiling is a hematocrit level of 54%. Go above that, and your doctor will typically lower your dose or pause treatment.
How often this happens varies. In one large trial, fewer than 1% of men on a low-dose gel exceeded the 54% threshold. In another trial using a different protocol, 22% of participants hit that level, and 5% had to stop treatment entirely. This is the main reason regular blood work isn’t optional. The American Urological Association recommends checking your complete blood count every 6 to 12 months while on therapy, and sooner if previous values were trending upward.
Prostate Health
For decades, men worried that taking testosterone would fuel prostate cancer. The current evidence doesn’t support that fear. The Mayo Clinic states plainly that testosterone itself is not likely to increase a person’s risk of developing prostate cancer, and studies of older men with low testosterone who received therapy did not show higher cancer rates than untreated men.
What can happen is that PSA levels (a protein marker used to screen for prostate issues) sometimes rise after starting therapy. Higher PSA prompts more biopsies, and more biopsies detect more cancers that might have gone unnoticed otherwise. So the apparent increase in prostate cancer diagnoses in some studies likely reflects better detection, not more disease. Scientists now describe this through a “saturation model”: prostate cells only need a certain amount of testosterone to grow, and once that threshold is met, adding more doesn’t accelerate anything.
That said, if you already have active prostate cancer, testosterone is off the table. It promotes growth in existing androgen-sensitive tumors. Men over 40 should have their PSA checked before starting therapy and monitored regularly afterward.
Fertility Suppression
This is one of the most underappreciated risks. Taking testosterone from an outside source signals your brain to stop telling your testes to produce their own. That shuts down or dramatically reduces sperm production. Most men on testosterone therapy end up with very low sperm counts or no detectable sperm at all.
The good news is that this is typically reversible. According to the American Society for Reproductive Medicine, sperm generally returns to the semen within about three months after stopping treatment, with no permanent damage. But if you’re trying to conceive or planning to in the near future, exogenous testosterone is considered contraindicated. Your doctor can discuss alternatives that raise testosterone levels without suppressing sperm production.
Liver Safety With Modern Formulations
Older oral testosterone pills, particularly methyltestosterone developed in the 1930s, were genuinely toxic to the liver. They caused abnormal liver enzymes, bile flow problems, and jaundice. That reputation stuck, and many people still assume any oral testosterone damages the liver.
Modern oral formulations use a different molecule, testosterone undecanoate, that gets absorbed through the intestinal lymphatic system rather than passing directly through the liver. Clinical trials of these newer pills show no clinically significant liver toxicity and no consistent increase in liver enzyme levels. One study even suggested a possible beneficial effect on liver fat. Injections and topical formulations bypass the liver entirely, so liver damage is not a meaningful concern with those delivery methods.
Who Should Not Take Testosterone
Beyond the situations already mentioned, the U.S. Department of Veterans Affairs maintains a detailed list of contraindications. Testosterone therapy is not appropriate for men with:
- Active breast cancer, which is hormone-sensitive and can be stimulated by testosterone
- Untreated severe sleep apnea, which already raises red blood cell levels and compounds the erythrocytosis risk
- Elevated, unevaluated PSA levels (above 4 ng/mL generally, or above 3 ng/mL in men with additional prostate cancer risk factors)
- Severe urinary symptoms from an enlarged prostate, since testosterone can worsen these
- A history of unprovoked blood clots or a diagnosed clotting disorder
- Severe liver disease or kidney failure
What Monitoring Looks Like
Safe testosterone use requires a structured follow-up schedule, not just a prescription and a handshake. Before starting, your doctor should check your total testosterone level (below 300 ng/dL is the standard diagnostic cutoff), complete blood count, and PSA if you’re over 40.
Once you start, the timeline for your first follow-up blood draw depends on the delivery method. Men using gels, patches, or nasal formulations should have testosterone levels rechecked two to four weeks in. Men on regular injections should wait several cycles, typically three to four, before testing, because levels need time to stabilize. After that initial check, testosterone and blood counts should be measured every 6 to 12 months for as long as you’re on therapy.
Bone and Body Composition Benefits
The safety conversation isn’t complete without the other side of the ledger. Men with genuinely low testosterone face real health consequences from leaving it untreated, including progressive bone loss. A long-term study published in the Journal of Clinical Endocrinology & Metabolism found that previously untreated men saw their spinal bone mineral density jump roughly 39% during the first year of therapy. Men who had already been on treatment for a year or more continued to gain bone density, though at a slower rate of about 15% over an average of four additional years. The men who started with the lowest bone density saw the largest improvements.
These gains held regardless of whether men used injections or topical testosterone. For men with confirmed hypogonadism, the bone protection alone can meaningfully reduce fracture risk over time, which is a concrete benefit that weighs against the monitoring burden and potential side effects.