Hormone replacement therapy

Hormone replacement therapy (HRT) is a therapy for women who have gone through age-related menopause or surgically-induced menopause (removal of ovaries and/or uterus due to disease), thus requiring additional hormones to replace the ones their bodies are no longer producing. There has been considerable concern in recent years due to links between long-term HRT in post-menopausal women and breast cancer. Combined estrogen–progestogen menopausal therapy is carcinogenic in the breast and endometrium of women.

HRT in transgender therapy
HRT is also prescribed to transgender individuals, who wish to ease gender dysphoria, improve gender euphoria, or neither at all in order to suppress naturally-occurring hormones and replace them with greater quantities of those which determine secondary-sex characteristics of the opposite physical sex, usually for the purpose of making their body match what they associate with their psychological gender identity.

According to the World Professional Association for Transgender Health's Standards of Care, a mental health professional (which is loosely defined by the Standards of Care as someone with "[clinical] training [...] within any discipline that prepares mental health professionals for clinical practice, such as psychology, psychiatry, social work, mental health counseling, marriage and family therapy, nursing, or family medicine with specific training in behavioral health and counseling") must diagnose a patient with gender dysphoria and provide a letter approving HRT in order for therapy to commence. However, as this process can take quite a while, and some mental health professionals may have unreasonable expectations, many self-medicate as HRT medications for transgender women are not controlled substances in most countries. However, for transgender men, testosterone is considered a Schedule III controlled substance.