Prometrium (Micronized progesterone) is a natural progesterone that has been broken down -- or micronized -- to enable your body to metabolize it more easily. Before this process was discovered, women couldn't take natural progesterone orally because it was absorbed badly and became inactive when swallowed. But now it's easily available, allowing you to get the benefits of natural progesterone in the ease of a pill.
Most often, you get micronized progesterone at a compounding pharmacy -- a pharmacy that formulates its own drugs according to a doctor's prescription. But in 1998, a micronized natural progesterone called Prometrium put out by the large pharmaceutical company Schering, became available, which is good news for women who found it difficult to find a compounding pharmacy in their area.
Briefly, the big plus about natural micronized progesterone is the lack of side effects. It's often prescribed to women who have had bad luck with progestins. In addition, it doesn't inhibit estrogen's raising of good cholesterol and may help build bone. All of this, plus the normal protective benefits of adding progesterone to your HRT, makes natural micronized progesterone a good choice.
The only real downside is cost -- natural micronized progesterone is usually much more expensive than Provera or the other progestins. In addition, a micronized progesterone from a compounding pharmacy may come in different bases which affects absorption. However, with the introduction of Prometrium from a large pharmaceutical company, both costs and standardization may improve.)
Prometrium is usually taken orally, however it can also be used as a vaginal suppository. In the latter case, the capsule is inserted directly in the vagina.
Prometrium contains peanut oil, anyone allergic to peanuts should not use this. However, micronized progesterone capsules from a compounding pharmacy can be made using a different type of oil than peanut oil.