Testosterone supplements carry real risks, and the answer to whether they’re safe depends heavily on what type you’re taking and whether you’re doing so under medical supervision. Prescription testosterone therapy for clinically low testosterone is a different category from over-the-counter “testosterone boosters” sold in supplement stores. Both come with concerns, but the risks differ significantly.
Prescription vs. Over-the-Counter: Two Different Risks
When most people search for testosterone supplement safety, they’re thinking about one of two things: prescription testosterone replacement therapy (TRT) prescribed by a doctor, or herbal “testosterone booster” supplements sold online and in retail stores. These are not the same product, and they don’t carry the same risks.
Prescription TRT delivers actual testosterone into your body, which means it has powerful hormonal effects, both intended and unintended. Over-the-counter boosters typically contain herbal blends that claim to raise your natural testosterone levels, though many have little clinical evidence behind those claims. The danger with OTC products is different: some contain hidden ingredients, including anabolic steroids that aren’t listed on the label, and these can cause serious organ damage without you even knowing what you’ve taken.
Heart and Blood Pressure Concerns
Cardiovascular risk has been the biggest safety question around testosterone therapy for over a decade. A widely cited Veterans Affairs study found that men on testosterone therapy had a 29 percent greater risk of death, heart attack, or stroke compared to men not using it, over roughly two and a half years of follow-up. At the three-year mark, 26 percent of men on testosterone had died or experienced a heart attack or stroke, compared to 20 percent who weren’t on therapy.
More recently, a large clinical trial called TRAVERSE provided clearer data, and the FDA updated its labeling for all testosterone products in February 2025 based on those results. The FDA actually removed a boxed warning about increased cardiovascular risk that had been on testosterone labels, suggesting the earlier fears may have been overstated for some populations. However, the FDA simultaneously added new warnings about increased blood pressure, which testosterone therapy can raise. So the cardiovascular picture is more nuanced than a simple “safe” or “dangerous” verdict.
Blood Thickening Is a Common Side Effect
One of the most predictable risks of testosterone therapy is that it stimulates your bone marrow to produce more red blood cells. This is a normal biological response, but when red blood cell levels climb too high, your blood becomes thicker and harder to pump. That raises your risk for blood clots, stroke, and other cardiovascular events.
Doctors track this using a measurement called hematocrit, which reflects the percentage of your blood volume made up of red blood cells. The American Urological Association recommends investigating if hematocrit exceeds 50 percent, and reducing or stopping testosterone if it reaches 54 percent or higher. The Endocrine Society sets a similar threshold, recommending that testosterone be withheld above 54 percent until levels normalize. In practice, about 5 percent of men on therapy reach the point where medical intervention is needed, sometimes involving therapeutic phlebotomy (essentially donating blood to thin it out).
This is one of the main reasons testosterone therapy requires regular blood work. During the first three to six months, most men have labs checked every six to eight weeks. Once levels stabilize, monitoring typically shifts to every six to twelve months.
Fertility Can Be Severely Affected
This catches many men off guard. Taking testosterone from an outside source signals your brain to stop telling your body to produce its own. When that happens, sperm production drops dramatically. Research shows that exogenous testosterone can cause a complete absence of sperm in 65 percent of men with normal sperm counts within just four months of use.
For men who want to have children now or in the future, this is one of the most important safety considerations. Sperm production usually recovers after stopping testosterone, but the timeline varies and full recovery isn’t guaranteed for everyone. If fertility matters to you, this should be part of any conversation before starting therapy.
Prostate Cancer Risk Is Lower Than Once Feared
For years, testosterone therapy was considered risky for prostate health because many prostate cancers use testosterone to grow. The current evidence tells a more reassuring story. According to the Mayo Clinic, testosterone itself does not appear to increase a person’s risk of developing prostate cancer. Studies of older men with low testosterone who were treated with therapy did not show higher rates of prostate cancer compared to untreated men.
The leading explanation is called the saturation model: prostate cancer cells need testosterone to grow, but only up to a certain level. Once that threshold is reached, adding more testosterone doesn’t accelerate growth. Even for men who have been successfully treated for prostate cancer with no signs of recurrence, testosterone therapy doesn’t seem to increase the risk of the cancer returning. That said, doctors still monitor PSA levels (a marker of prostate activity) as a standard part of ongoing blood work during therapy.
OTC Boosters Pose a Different Danger
Over-the-counter testosterone boosters are classified as dietary supplements, which means they don’t go through the same safety testing as prescription drugs before reaching store shelves. The most serious risk with these products isn’t the herbs listed on the label. It’s what’s hidden inside them.
Many bodybuilding and hormone-related supplements have been found to contain anabolic steroids or other undisclosed chemicals. These hidden ingredients can cause severe liver damage. Research from Michigan Medicine found that bodybuilding supplements contaminated with anabolic steroids can lead to severe cholestatic hepatitis, a form of liver injury that can take months to resolve. In one case series, a popular supplement called Hydroxycut caused severe hepatitis in 12 patients, with liver injury developing after an average of just eight weeks of use.
Green tea extract, a common ingredient in many multi-ingredient supplements marketed for weight loss and performance, has also been linked to liver injury. Six patients who took products containing concentrated green tea extract developed liver damage, and four of them became severely jaundiced. The takeaway: just because a product is sold without a prescription doesn’t mean it’s gentle on your body. Unregulated supplements can be more dangerous than the prescription therapy they’re trying to replace.
Who Should Avoid Testosterone Entirely
Certain medical conditions make testosterone supplementation particularly risky. Obstructive sleep apnea is one of the most significant. Testosterone therapy is typically contraindicated in people with sleep apnea or those at high risk for it, because testosterone can worsen the condition. Since sleep apnea itself raises cardiovascular risk, the combination is especially concerning.
Beyond sleep apnea, doctors also carefully evaluate men with existing heart disease, a history of blood clots, significantly elevated red blood cell counts, or untreated prostate conditions before considering therapy. Testosterone also raises estrogen levels through a conversion process in the body, which can cause fluid retention, mood changes, and breast tissue growth in some men. These effects are monitored through blood work and managed with dose adjustments when needed.
What Safe Use Actually Looks Like
If you’re considering testosterone therapy, safety depends on three things: having a legitimate medical reason (confirmed low testosterone with symptoms), using a regulated prescription product, and committing to regular monitoring. The blood work schedule matters. During the first several months, your doctor will track your testosterone levels, red blood cell counts, estrogen, PSA, liver enzymes, and lipid panels to catch problems early. Stable patients continue monitoring at least once or twice a year.
For OTC testosterone boosters, there’s no reliable way to confirm what’s actually in the product or whether the ingredients do what they claim. If you’re using one of these products and experience unusual fatigue, yellowing skin, dark urine, or abdominal pain, those are signs of possible liver injury that need immediate attention.