What are the benefits and risks of taking progesterone?

There have been no well-designed studies of the role of progesterone (progestogens) in feminising hormone regimens. Everyone is different and as such so are the effects of any medication including progesterone. The feminisation effect of progesterone is variable and may not work for everyone.

Breast development
Many transgender women and doctors report improved breast and/or areolar development, mood, or libido with the use of progestogens. There is some anecdotal evidence that progesterone could increase breast size in trans women, or increase the size of the areola (skin around the nipple) which can make the breast tissue appear more developed.

Skin and hair
Progesterone acts on the pituitary gland in the brain, telling it to turn off signals to the testicles. This stops cells in the testicles from producing testosterone, which means there is less dihydrotestosterone to make male characteristics grow. Skin becomes less oily, facial and body hair becomes lighter and less coarse. This suggests that progesterone may aid more rapid feminisation when incorporated into the hormone therapy regime for trans women.

Weight
Progesterone influences weight in two ways; it increases distribution of body fat and, at the same time, it increases protein breakdown. An increase in body weight has been recorded in 0.1% to 1% of people on progesterone after 6 to 12 months of continuous use. This equates to around 2kg of weight gain. There have also been reports of weight loss but the frequency is unknown.

There is no evidence to suggest that using progestogens are harmful. In reality some patients may respond favourably to progesterone while others may find negative effects on mood.

There were some concerns from the Women's Health Initiative (WHI) regarding heart and breast cancer risks, but these risks were not associated with the use of bioidentical progesterone. Utrogestan and Cyclogest are not known to be harmful or associated with risk.

The overall feeling is that the risks of using progesterone in transgender women are likely to be minimal or even absent.

Progesterone influences weight in two ways; it increases distribution of body fat and, at the same time, it increases protein breakdown. An increase in body weight has been recorded in 0.1% to 1% of people on progesterone after 6 to 12 months of continuous use. This equates to around 2kg of weight gain. There have also been reports of weight loss but the frequency is unknown.