These were designed to make HRT as easy as possible -- by combining both estrogen and a progestin in one tablet. Both Prempro and Premphase contain Premarin and Cycrin in the standard dosages you’d get if you took them individually.

With Prempro, you take both estrogen and progestin every day -- which emulates continuous therapy. With Premphase, you take estrogen daily, and the progestin for the last two weeks of every month -- which is cyclical therapy.

There’s really no difference between taking one of these combination pills or taking two separate estrogen and progestin tablets. The only difference is the simplicity. You take one tablet every day and don’t have to think about what day of your cycle it is (if you’re on cyclical HRT) or don’t have to worry about getting two prescriptions filled. That’s the upside, of course. As for the downside -- it’s the same as if you were taking Premarin and a progestin separately. Again, there’s a good chance of PMS-like side effects from the progestin; and you face the negatives of Premarin as well.

Another more recent -- and more serious -- downside:  a recent large scale study that tracked over 16,000 post-menopausal women found that long term use of Provera increased the risk of breast cancer, heart attack and stroke.  On an individual basis, the risk increased by about one-tenth of 1% per year....but the Prempro part of study was discontinued due to this risk.  It was hypothesized that the risk of these problems accumulated over time -- so the longer one is on Prempro, the more risk one is exposed to. It's unclear whether these risks apply to a younger woman who's on Prempro due to premature ovarian failure or POF.  For more on the findings of this study, see the article on the WHI Study.