Testosterone is used medically to treat men whose bodies don’t produce enough of it on their own, and it plays a central role in muscle growth, bone strength, red blood cell production, and sexual function in both men and women. Beyond its FDA-approved uses, testosterone is also prescribed off-label for low sexual desire in postmenopausal women and as part of masculinizing hormone therapy for transgender men.
What Testosterone Does in Your Body
Testosterone is often thought of as a sex hormone, and it is, but it does far more than drive libido. It binds to receptors in muscle cells and stimulates protein synthesis, which is why it’s a key regulator of muscle mass and strength. It’s also essential for bone health. During puberty, testosterone helps bones reach their peak density, and it continues to maintain that density throughout adulthood. When levels drop significantly, both muscle and bone loss accelerate.
Testosterone also drives red blood cell production. It signals your kidneys to produce more of the hormone that triggers red blood cell growth, while simultaneously making more iron available for your blood to use. In studies, testosterone administration increased that signaling hormone by about 58% within the first month. This is why men naturally carry higher red blood cell counts than women, and why testosterone therapy can sometimes push those counts too high.
In the brain, testosterone regulates sexual desire in both men and women by affecting regions responsible for sexual motivation and arousal. It also influences mood and energy. Low levels are commonly associated with fatigue, irritability, and difficulty concentrating.
FDA-Approved Uses in Men
The FDA approves testosterone products only for men who have low levels combined with an underlying medical condition. This includes situations where the testicles can’t produce testosterone normally, whether from genetic conditions, chemotherapy damage, or problems with the brain structures (the hypothalamus and pituitary gland) that signal testosterone production. The normal range for testosterone in non-obese men aged 19 to 39 is 264 to 916 ng/dL, based on harmonized data from European and American populations.
This distinction matters: having a testosterone level on the lower end of normal, without an associated medical condition, is not an approved reason for treatment. The FDA has been explicit that testosterone products are not approved for age-related decline alone, despite how commonly they’re prescribed for that purpose.
Off-Label Use for Women
Testosterone isn’t FDA-approved for use in women, but it’s widely prescribed off-label for low sexual desire in postmenopausal women. Clinical evidence supports transdermal testosterone (applied to the skin as a gel or cream) at roughly one-tenth the dose used in men. For context, a standard men’s gel tube contains 50 mg of testosterone. The starting dose for women is typically around 5 mg, with the option to increase to 10 mg if needed. The goal is to restore testosterone to the range a woman would have had before menopause, not to reach male levels.
A pilot study of transdermal testosterone therapy in peri- and postmenopausal women found significant improvements in both mood and cognition after four months. About 47% of women reported mood improvements, while 39% noticed better cognitive function.
Masculinizing Hormone Therapy
For transgender men and some nonbinary individuals, testosterone is used to develop masculine secondary sex characteristics. The expected changes include increased facial and body hair, a deeper voice, greater lean muscle mass, reduced body fat, cessation of menstruation, and increased sexual desire. Beyond physical changes, testosterone therapy in this population is associated with reductions in gender dysphoria, perceived stress, anxiety, and depression. These changes develop gradually over months to years, with voice deepening and body hair growth among the slower effects.
How Testosterone Is Delivered
Testosterone comes in several forms, each with a different schedule and experience:
- Transdermal gels and patches: Applied daily. Patches are worn every 24 to 48 hours and bring levels into the normal range for over 85% of users. Gels are rubbed into the skin, usually on the shoulders or upper arms.
- Intramuscular injections: The most common injectable forms are given every one to two weeks. A longer-acting version requires injection only about four times per year, with doses at weeks 0 and 4, then every 10 weeks after that.
- Subcutaneous pellets: Small pellets are implanted under the skin and replaced every three to four months.
- Intranasal gel: Applied inside the nose three times daily.
- Oral capsules: Taken by mouth, though less commonly used than other methods.
The choice between these options typically comes down to how often you want to deal with dosing, whether you’re comfortable with injections, and how steady you want your hormone levels to be. Daily applications like gels maintain more stable levels, while injections can create peaks and valleys between doses.
Risks and Side Effects
The most common medical concern with testosterone therapy is a condition called polycythemia, where red blood cell counts climb too high. This happens in over 20% of men on therapy and can increase the risk of blood clots, stroke, and heart attack. If your red blood cell concentration rises above 54%, treatment is typically paused until levels return to normal. Baseline blood work before starting therapy and regular monitoring afterward are standard practice.
Sleep apnea is another recognized risk. Some men develop it after starting testosterone, and it resolves when treatment stops. For men who already have sleep apnea, testosterone can worsen symptoms. Untreated obstructive sleep apnea is actually a contraindication to starting therapy in the first place.
Cardiovascular risk has been debated for years. Earlier concerns about testosterone promoting artery-clogging plaque have softened as more data has come in. Current evidence suggests a neutral to slightly beneficial effect on cardiovascular events for most men, though those with limited heart function may experience fluid retention that strains the cardiovascular system.
Who Should Not Take Testosterone
Several conditions rule out testosterone therapy entirely. These include a history of breast cancer, prostate cancer, uncontrolled heart failure, and a heart attack or stroke within the past six months. Men with a red blood cell concentration already above 50%, an undiagnosed prostate nodule, or an elevated PSA level above 4 ng/mL are also not candidates. Testosterone suppresses sperm production, so men who are actively trying to conceive should not use it.