Excessive bleeding is a troublesome and sometimes dangerous side effect of hormone replacement therapies (HRT) for many women.

A recent national clinical trial, published in the November edition of the Journal of Obstetrics and Gynecology, showed that two of the most common HRT combinations (estrogen plus medroxyprogesterone acetate and estrogen plus micronized progesterone) can cause days of intense bleeding. Previous studies have shown that unacceptable bleeding is the reason most women discontinue HRT during the first year of therapy.

The report comes from the PEPI trial that studied 875 women over a three year period at seven sites in the United States. Participants took either a placebo, estrogen alone, estrogen plus a continuous form of MPA, estrogen plus a cyclical form of MPA, or estrogen plus a cyclical form of MP. The estrogen used in the study was conjugated equine estrogen, the most common form used for HRTs.

A cyclical regimen uses estrogen daily and the progesterone for 12 days per 28 day cycle, mimicking a menstrual cycle with bleeding near the end of the progesterone phase. A continuous HRT regimen uses the same dose of estrogen and progesterone every day and is expected to cause less bleeding.

Excess bleeding was considered to be any bleeding on a continuous regimen, or more than one episode per month with cyclical treatment. While all types of therapy caused bleeding, the researchers continually stressed the fact that the MP combination was less harmful.

A press release distributed by the University of California, San Diego (where the researchers work) also attempted to spin the results to indicate that the MP therapy was better than the MPA combination. The release noted that the MPA had the lowest number of "unexpected bleeding episodes," but failed to give specifics about the percentage of women who suffered the side effect -- or the seriousness of the problem.

That isn't surprising. The current study was supported in part by an unrestricted educational grant from Solvay Pharmaceuticals, maker of a popular and profitable MPA therapy drug.