Systemic progesterone therapy--oral, vaginal, injections and even transdermal?

Several medicinal products containing progesterone are in widespread use orally for protection of the endometrium during concurrent oestrogen treatment, and injections or vaginally for support of luteal function during assisted reproduction. These indications have been established in extensive clinical testing programmes. In addition, the results of recent studies and meta-analyses suggest that vaginal progesterone is an effective method for preventing premature births in singleton pregnancies in women with a shortened cervix. In US, 17α-hydroxyprogesterone caproate is licensed to reduce the risk of preterm birth in women with a singleton pregnancy who have a history of singleton spontaneous preterm birth. There is insufficient evidence from scientific studies to substantiate the transdermal application of progesterone. In particular, these preparations should not be used to oppose the effects of oestrogen on the endometrium, because even with low doses of estradiol a reliable progestogenic effect to protect the endometrium has not been proved. On the other hand, the application of transdermal progesterone preparations alone is not known to pose any risks to health.