Can progesterone treat premenstrual syndrome? Poor research methods leaves important question unanswered

Five in every one hundred women suffer premenstrual symptoms at some time in their lives that are severe enough to interfere with their lives. One possible cause of the symptoms is the drop in progesterone that comes before menstruation. A suggested treatment, therefore, is to give women extra progesterone. But many health professionals doubt whether this treatment works.

To see if the research evidence can help resolve this, Cochrane Review Authors examined 17 different studies before performing a more detailed analysis of the data from the two trials which met their eligibility criteria. Of these, one trial of ‘better quality’ concluded that progesterone was more effective than placebo.

The main problem with assessing the benefit of progesterone is that 15 of the 17 trials had to be excluded for one or more important reasons. Some did not screen women for psychiatric disorders or persistence of symptoms after their menstrual periods, and others had to be excluded because the diagnosis of PMS was based on less than two cycles of symptom records. Probably because they needed to be run over many months, many trials also had a high drop out rate.

“The Review has revealed more about the difficulties inherent in the study of PMS and consequent deficiencies in method, than about the efficacy of progesterone in treating it,” says Lead Review Author Olive Ford former honorary Research Officer for the National Association for Premenstrual Syndrome.

Knowing whether progesterone is a useful treatment is complicated by the fact that treatments for PMS generally show large placebo effects. The Review Authors describe how some trials involving other therapies have found the placebo to have more effect than the treatment.

The Review points out that any women who do use progesterone need to be told of the mild side effects. These can include changes in menstrual cycle length and a tendency to become drowsy. In addition one woman who had believed herself to be infertile, conceived when taking progesterone, out of a total of about 650 women in all the trials examined.