New data from Australia add to the growing scepticism about the effects of rub-on progesterone creams as a miracle cure for everything from menopausal symptoms to osteoporosis.

Researchers from the Sydney Menopause Centre conducted a clinical trial using transdermal oestrogen and progesterone on 27 postmenopausal women, aged 50 to 65 years. All the women were given continuous oestrogen via a transdermal patch for a cycle of 12 weeks. The women were then randomly allocated 16 mg, 32 mg or 64 mg of micronised progesterone daily for 14 days during the second half of four 28-day cycles.

The idea of the study was to determine whether 'natural' progesterone could replace the progestogens used with oestrogen in hormone replacement therapy (HRT). Many women, leery of progestogens, have been substituting rub-on progesterone with their HRT.

Endometrial biopsy samples were obtained before treatment on day 14 of the first cycle of transdermal oestrogen, and on day 27 or 28 of the third cycle of micronised transdermal progesterone. The use of micronised progesterone, even at the highest concentrations, did not increase circulating blood progesterone concentrations enough to induce any change in the endometrium. This suggests that claims that rub-on progesterone protects against endometrial cancer and other abnormalities must be treated with caution.

It also adds weight to previous studies which concluded that rub-on progesterone is poorly absorbed (Lancet, 1999; 354: 1447-8).