In transgender men, or transmasculine people (FTM), the most common medication used for transition is testosterone. Administration of testosterone (via transdermal or intramuscular routes) lowers serum estradiol levels, raises serum testosterone levels, and results in the development of typical male secondary sex characteristics. Irreversible changes include: deepening of the voice, increase in facial and body hair growth, clitoral enlargement (clitoromegaly), and thickened facial bone structure. Reversible changes include amenorrhea, male-pattern fat distribution, increased muscle mass, vaginal atrophy, and male-pattern baldness. Some trans men also describe changes in emotions (e.g., inability to cry, increased anger) as well as increased libido. Adverse effects can include elevations in blood pressure, polycythemia, worsening of lipid profile, elevations in glucose, elevations in transaminases, acne, and effects on fertility (although testosterone is not an effective contraceptive as it does not interrupt ovulation, so pregnancy can still occur).
Finasteride can also be used to prevent male-pattern baldness in transgender men; however this will likely slow or decrease secondary hair growth, and may slow or decrease clitoromegaly.
In transgender women or transfeminine people (MTF), the most commonly used medications are estrogens and anti-androgens. Administration of estrogen (via oral, sublingual, transdermal or intramuscular routes) lower serum testosterone levels, raises serum estradiol levels, and results in the development of typical female secondary sex characteristics including: breast growth and female-pattern fat distribution as well as causing testicular atrophy (ultimately resulting in erectile dysfunction and infertility). These are largely reversible. Some trans women also describe changes in emotions (e.g., more tearful) as well as decreased libido. Adverse effects can include increased risk for thrombosis, elevations in blood pressure, elevations in prolactin (rarely including development of a prolactinoma), increased number of migraines, elevations in transaminases and effects on fertility (although estrogen is not an effective contraceptive). Estrogens will NOT heighten voice pitch, decrease facial hair, change facial bone structure, or reverse male-pattern baldness. Other methodologies would need to be employed (e.g., voice training, electrolysis or laser hair removal, facial feminization surgery).
Anti-androgens (i.e., spironolactone, flutamide, finasteride) are also commonly used in trans women who have not had an orchiectomy. These medications block the effects of testosterone, resulting in decreased erectile function and allowing estrogen to development typical female secondary sex characteristics.
Progesterones are largely converted to testosterone and may impede transition. In addition, some studies are showing a possible increased risk for cardiovascular disease and/or breast cancer with their use. However, in some cases, it may be indicated to maximize breast growth.
Not all transgender patients will want to take medications for gender transition and the risks, benefits and alternatives should be discussed with each individual along with their personal goals for transition to determine the right course.