A study to look at hormonal absorption of progesterone cream used in conjunction with transdermal estrogen.

Natural progesterone creams are gaining popularity as a possible treatment for menopausal symptoms, and many women may be using them with estrogen. We planned to evaluate, using an open plan study, the systemic absorption of a combination of transdermal estrogen and progesterone. Women applied transdermal progesterone 40 mg and transdermal estrogen 1 mg daily over 48 weeks. Women were assessed at intervals of 12 weeks. Significant increases in plasma levels of progesterone and estradiol were seen after 12 weeks, although only low plasma progesterone levels were found (median 2.5 nmol/l) and no further increase was noted over the remainder of the study period. A significant correlation was found between plasma levels of the two hormone (r = 0.315, p = 0.045). Women reported significant reductions in menopausal symptoms, as measured by the Green Climacteric Scale, after 24 and 48 weeks of combined treatment. There may be similar mechanisms of absorption of the two hormones, although the doses used in our study produced sub-luteal levels of progesterone. There was no evidence of accumulation of progesterone with time, and further study is needed to assess the efficacy and safety of this combination of hormones.