Dear Catherine,
As long as the pill contains progesterone and not an artificial progestin, then it is safe and can be effective at preventing miscarriages. Prometrium is a brand name for progesterone; feel confident taking it.
Progesterone is most effective when given by intramuscular injection because higher levels are achievable in the body. The second most effective is in sustained release vaginal suppository form because the vagina is a “direct route,” via blood vessels, to the uterus. Sustained release oral pills are next and Prometrium, which is immediate release micronized progesterone, the lowest.
Prometrium can cause sleepiness so it is usually dosed at night. The vaginal suppositories can cause vaginal dryness.
In health,
George Delgado, M.D., F.A.A.F.P.