Oral administration of micronized progesterone: a review and more experience

Historically, oral progesterone has been regarded clinically ineffective because of its poor absorption and rapid clearance. Recent evidence suggests that an oral micronized form of natural progesterone is readily absorbed, produces luteal phase serum concentrations, provokes an end-organ response, and has no detrimental effect on the lipoprotein profile. Thus it is considered by many to be an attractive alternative to synthetic progestin. We evaluated the effects of a single oral dose of micronized progesterone 300 mg in eight healthy postmenopausal women. The maximum serum concentration ranged from 15.72-625.98 ng/ml. The extent of absorption increased with increasing age. The reviewed literature and our data indicate considerable intersubject variability in the extent of progesterone absorbed after administration of oral micronized progesterone.