Testosterone therapy can improve muscle mass, sex drive, and energy in men with clinically low levels, but it also carries real trade-offs including fertility suppression, blood thickening, and skin changes. Whether the benefits outweigh the risks depends largely on your starting testosterone level and what you’re hoping to achieve. A clinical diagnosis of low testosterone typically means a total level below 300 ng/dL, the threshold recommended by the American Urological Association.
Improved Body Composition
One of the most consistent benefits of testosterone therapy is a shift in body composition: more lean muscle, less fat. Research from the U.S. Department of Veterans Affairs found that men gained fat-free mass (mostly lean muscle) over 18 months of treatment regardless of where their testosterone started. Men with the lowest baseline levels, under 264 ng/dL, saw the largest gains, likely because their muscles were more sensitive to the hormone after prolonged deficiency. But even men closer to the 300 ng/dL cutoff added measurable lean tissue.
Bone density also improves, particularly in men with very low levels. Studies show that men starting below 200 ng/dL experience the greatest increases in spine bone mineral density. For older men at risk of fractures, this can be a meaningful protective effect.
Better Sexual Function
Low testosterone is one of the most common treatable causes of low libido in men. In a year-long study covered by the Endocrine Society, men on testosterone therapy showed consistent improvements in sexual desire and in 10 of 12 measures of sexual activity, including frequency of intercourse, masturbation, and nighttime erections. Men who received a placebo saw no significant change over the same period. For many men, this improvement in sexual function is the primary reason they seek treatment in the first place, and the evidence here is strong.
Cardiovascular Risk: Lower Than Once Feared
For years, one of the biggest concerns about testosterone therapy was heart safety. A large trial published and reviewed by the American College of Cardiology put this question to a rigorous test. Over 5,200 men aged 45 to 80, all with pre-existing heart disease or significant cardiovascular risk factors, were randomly assigned to testosterone or placebo. The rate of major cardiovascular events (heart attack, stroke, or cardiovascular death) was 7% in the testosterone group and 7.3% in the placebo group. Secondary endpoints, including the need for procedures like stenting, were also similar between groups.
This doesn’t mean testosterone is heart-protective. It means that for men who genuinely have low levels, treatment doesn’t appear to add cardiovascular danger beyond their baseline risk. That said, this trial specifically enrolled men with confirmed low testosterone. Using testosterone when your levels are already normal is a different situation with far less safety data.
Fertility Suppression
This is one of the most important and most overlooked downsides. Testosterone therapy typically leads to either very low sperm counts or no sperm at all in the ejaculate, according to the American Society for Reproductive Medicine. The reason is straightforward: when you supply testosterone from outside the body, your brain stops signaling the testes to produce it internally, and that same signaling pathway drives sperm production.
For men who want to have children now or in the future, this is a serious consideration. Sperm production often recovers after stopping therapy, but recovery isn’t guaranteed and can take many months. If fertility matters to you, this needs to be part of the conversation before starting treatment, not after.
Blood Thickening
Testosterone stimulates your bone marrow to produce more red blood cells. In moderation, that can improve energy and oxygen delivery. Taken too far, it raises your hematocrit (the percentage of your blood made up of red cells) to levels that increase the risk of blood clots, stroke, and other vascular problems.
Guidelines from the American Urological Association recommend investigating if hematocrit exceeds 50% and reducing or pausing therapy at 54%. The Endocrine Society sets a similar threshold, recommending that testosterone be withheld above 54% until levels normalize. This is why regular blood work is a non-negotiable part of testosterone therapy. Most prescribing doctors check hematocrit every few months, especially in the first year.
Skin and Hair Changes
Acne and hair loss are among the more visible side effects. Testosterone converts to a more potent hormone in the skin and hair follicles, which can trigger breakouts and accelerate male pattern baldness in men who are genetically predisposed. A meta-analysis in the Journal of the American Academy of Dermatology, looking at transgender men on testosterone therapy, found that roughly 12.5% developed significant hair thinning. In cisgender men who already have some degree of thinning, testosterone therapy can speed up the process noticeably. These effects are dose-dependent, meaning they tend to be worse at higher levels.
Prostate Safety
The relationship between testosterone and prostate cancer has been a source of anxiety for decades, but the current medical consensus has shifted substantially. According to the Mayo Clinic, current evidence does not support a link between testosterone therapy and the development of new prostate cancer. Multiple studies of older men with low testosterone found no higher rates of prostate cancer in those treated compared to those who were not.
Even in men who have already been treated for prostate cancer, studies suggest testosterone therapy doesn’t appear to increase the risk of recurrence. One thing that does happen is that PSA levels (a blood marker used to screen for prostate issues) can rise after starting testosterone, which can cause alarm on routine lab work even when nothing is wrong. Knowing this in advance helps avoid unnecessary worry.
Sleep Apnea
There’s a modest connection between testosterone therapy and obstructive sleep apnea. In a study of over 6,400 men with low testosterone on therapy, 14% were diagnosed with sleep apnea after starting treatment, compared to a 12% baseline rate among all men with low testosterone. That’s a small absolute difference, but if you already snore heavily, are overweight, or have other risk factors for sleep apnea, it’s worth monitoring. Symptoms to watch for include waking up feeling unrefreshed, daytime sleepiness, and a partner noticing pauses in your breathing at night.
How Delivery Method Matters
Testosterone comes in several forms: injections (usually every one to two weeks), daily topical gels, and skin patches. These aren’t interchangeable in terms of side effects. Injections create sharp peaks of testosterone shortly after the shot, followed by a gradual decline. Those spikes can amplify side effects like mood swings, acne, and blood thickening. Gels and patches deliver a steadier, more physiologic level throughout the day.
A study from UNC’s Gillings School of Global Public Health found that injections carry a greater risk of adverse effects than gels or patches, likely because of these pharmacokinetic differences. The trade-off is convenience: injections are less frequent, while gels require daily application and carry a small risk of transferring testosterone to a partner or child through skin contact. Many men start with one method and switch based on how they respond.