UPA is a drug in a class of medications known as selective progesterone receptor inhibitors. This medication is already in use as an emergency contraceptive. Unlike an "abortion pill," UPA simply prevents the release of the egg from the fallopian tubes. It stops fertilization rather than implantation by making the ovaries less sensitive to progesterone. The lining of the uterus, that is, the endometrium, is also sensitive to progesterone. Medical researchers have observed that stopping the action of progesterone on the endometrium prevents month-to-month growth in uterine fibroids. The fibroids are still somewhat larger during the first half of the menstrual period due to the action of estrogen, but they do not grow during the second half of the menstrual period in ways that increase bleeding and pain.
Treating fibroids with surgery, of course, reduces fertility by shrinking the available surface of the uterus for the implantation of the fertilized egg. Treating fibroids with medications to lower estrogen levels threatens bone health. UPA, however, acts selectively on the lining of the uterus to cause fibroids to shrink month to month, rather than grow month to month, although there continue to be variations in the size of fibroids during the menstrual cycle. Some women taking a higher, 20 mg dose of UPA for several months had no menstrual bleeding at all. While this indicates improvement in fibroids, it does not indicate immediate restoration of fertility. Probably women will need to use the drug for 4 to 6 months to shrink fibroids without surgery, and then they will need to be off the drug for 2 or 3 months to regain fertility. Other treatments for fibroids, however, can leave fertility permanently impaired. UPA is manufactured by the Swiss pharmaceutical company PregLem SA. Results of testing are likely to be submitted to regulatory agencies in the EU and USA later this year.