Sex relieves menstrual cramps. This has been documented in various studies and was reported in a Planned Parenthood report. Planned Parenthood also reported that orgasm causes a surge in the calming hormone oxytocin (a natural chemical in the body that surges before and during climax) and feel-good hormones, such as endorphins, that may act as sedation. They cite a study which found that 32% of 1,866 U.S. women who reported masturbating in the previous three months did so to help them go to sleep. Another study reported that 9% of about 1,900 U.S. women who reported masturbating in the previous three months cited relief of menstrual cramps as a motivation.