Oral contraceptives and endometriosis.

Since retrograde menstruation has been proposed as a major factor in the development of endometriosis, contraceptive methods that influence menstrual flow may increase the risk of endometriosis. The literature on a possible association between oral contraceptive (OC) use and endometriosis is conflicting. Recent reports, including the 1994 Oxford Family Planning Association Study and the Royal College of General Practitioners OC Study, suggest that current OC users have a lower risk of endometriosis, while former users may have an increased risk. The observed increase in risk after OC discontinuation presumably reflects a selection bias in which women who choose to take OCs may be selected or self-selected to use this method because of problems with their menstrual cycle. Since endometrial tissue proliferates in response to estrogen, low-dose OCs with progestin are recommended for the prevention or suppression of endometriosis.