Testosterone replacement is a form of therapy used to treat low levels of the hormone testosterone in men. It may also be part of treatment to stimulate puberty in adolescent males who experience delayed puberty. 

Symptoms of testosterone deficiency in males, also known as male hypogonadism, include a lower libido, depression, low bone density resulting in brittle bones, low sperm production, decreased muscle mass, and a decrease in facial and body hair. 

Primary male hypogonadism is caused by a problem in the testicles. The secondary form of the condition is caused by a problem in the pituitary gland or hypothalamus, resulting in the release of insufficient quantities of testosterone.

Testosterone replacements in the form of androgens may be administered in a variety of forms, including injections, gel, patches, gum, nasal gels, and pellets implanted under the skin.