Progesterone (aka P4 or just prog) is the main progestogen in the human body, affecting tissues in the breasts, reproductive system, skin, brain and other organs.[1]

There are currently no studies which directly show increase breast growth. However this may partially be due to small sample sizes and a lack of standardization surrounding dosages and administration. Considering it's one of the key hormones in cis women and has known effects on breast and other tissues it is still recommended to use. The typical dose for trans women is 100-200mg a day.

Do not use oral pills

In the past it was believed that prog oral pills are sufficient to achieve a female levels but it's now known that the first-pass liver effect after oral ingestion of progesterone creates metabolites such as pregnanolone and allopregnanolone which interfere with blood tests and cause misleading results, overestimating the levels of progesterone by 5-8 times[2]. Most labs use standard immunoassay (IA) procedures and unless it's stated to use chromatographic separation (CS) or liquid chromatography-mass spectrometry (LC-MS) the blood test for oral prog is unreliable. Because of this it is recommended to use other routes of administration.

Rectal administration (boofing)

The current most common way for trans women to take progesterone is as a suppository as it has high bioavailability. This can be done by taking your suppository, covering it with a small amount of water/lube/moisturizer and then using your finger to push it up into your anus past the sphincter where it will be dissolved in the rectum within a couple of hours (it's recommended you do this after a bowel movement).

Although not directly formulated for it, if you get oral progesterone pills there is a good chance that you can take them rectally. If the pill is squishy and feels like it contains oil, it is safe to take it rectally. If you are unsure, you can visit and search for the color, general shape, and numbers/letters on the pill. Once there, check for the following under inactive ingredients: gelatin, glycerin, water, peanut oil. These can help you determine if you have a gelatin/oil pill containing bioidentical/micronized progesterone. Alternatively, you can ask your doctor if the progesterone you were given is micronized or bioidentical.

Typical prog oil/gel pills which can be ingested rectally