The hormone replacement therapy that U.S. Army Pfc. Bradley Manning has requested alters the body's balance of sex hormones: estrogen for male-to-female and testosterone for female-to-male transitions. Sometimes, male-to-female patients will also be given progesterone, another steroid typically produced by the ovaries, as well as a testosterone blocker such as spironolactone.
"It basically initiates a second puberty. The full effects of that will typically take two to three years," said Marci Bowers, a gynecologist and surgeon who has performed hundreds of gender-change operations over the past decade.
Not all patients getting hormone replacement therapy have surgery, either because of the cost or personal preference.
Hormones are the chemical messengers of the body that travel through the bloodstream and send signals to various organs, affecting growth, metabolism, reproduction and mood. Continuous doses of female hormones will cause a male to see changes within the first few months of therapy, including softer skin, fat and muscle rebalancing, and breast development.
Those changes start to become irreversible within six to nine months. The effects of hormone therapy vary among individuals.
It is not known whether Manning will be allowed the medication while incarcerated.