Why is it that so little is known about PMS? First of all, there is no agreement on what PMS is. If investigators are referring to different sets of symptoms, how can studies be comparable? In fact, they are not. Not only are the symptoms different, but the timing of symptoms is different, Some studies describe symptoms that occur 7 to 10 days before the onset of menses, while others include symptoms that begin 14 days before the onset of menses and continue for 7 days after onset. This definition suggests that women may have PMS-related symptoms during 21 days of a 28-day cycle. I don't want to believe this-and I don't have to-because little scientific evidence exists to either support or refute this hypothesis.
Medicine and Health | Obstetrics and Gynecology | Women's Health
Copyright American Medical Women’s Association used with permission
PMS or perifollicular phase euphoria?.
Journal of the American Medical Women’s Association, 43