Testosterone replacement therapy is used to treat cases of testosterone deficiency in several disease conditions.

Indications for therapy

Testosterone replacement therapy is usually used to treat males who produce little or no testosterone, such as those with hypogonadism. A man is considered to have hypogonadism if the total serum testosterone level is less than 300 ng/dL in a morning sample. This lower limit may vary with age and is therefore usually an age- adjusted value.

Other possible indications include:

• Low testosterone levels in infertile males
• Loss of libido. In post-menopausal women, transdermal patches may be used to improve libido.
• Erectile dysfunction
• For penile enlargement
• For increasing height
• For stimulation of bone marrow and correction of anemia
• For stimulation of appetite
• For reduction of insulin resistance in diabetic patients
• To achieve male sexual characteristics in men who have had a sex change
• For the prevention of osteoporosis, heart disease, vascular diseases, depression, obesity, anxiety, anemia and neurological diseases such as Alzheimer's disease
• Athletes sometimes take testosterone to enhance their performance, strength, endurance and development.

Side effects

The replacement therapy may be in the form of injectable depots, transdermal patches, subcutaneous pellets, oral pills or gels. Adverse effects include acne, oily skin, sleep apnea, accelerated growth of prostate cancer and weight gain.

Routes of administration

Testosterone can be administered via several routes including:

• By injection
  Usually preparations such as testosterone cypionate or testosterone enanthate in oil are injected into the muscles (intramuscular injections)
• Pills, patches or gels
• Testosterone preparations may also be administered in the form of transdermal gels, patches or can be taken as a tablet