Testosterone (T) is a medication and naturally occurring steroid hormone.[7] It is used to treat male hypogonadism, gender dysphoria, and certain types of breast cancer.[7][8] It may also be used to increase athletic ability in the form of doping.[7] It is unclear if the use of testosterone for low levels due to aging is beneficial or harmful.[9] Testosterone can be used as a gel or patch that is applied to the skin, injection into a muscle, tablet that is placed in the cheek, or tablet that is taken by mouth.[7]

Common side effects of testosterone include acne, swelling, and breast enlargement in men.[7] Serious side effects may include liver toxicity, heart disease, and behavioral changes.[7] Women and children who are exposed may develop masculinization.[7] It is recommended that individuals with prostate cancer not use the medication.[7] It can cause harm to the baby if used during pregnancy or breastfeeding.[7] Testosterone is in the androgen family of medications.[7]

Testosterone was first isolated in 1935, and approved for medical use in 1939.[10][11] Rates of use have increased three times in the United States between 2001 and 2011.[12] It is on the World Health Organization's List of Essential Medicines.[13] It is available as a generic medication.[7] In 2020, it was the 172nd most commonly prescribed medication in the United States, with more than 3 million prescriptions.[14][15]