Flumedroxone is a progestative agent. It is a pregnane derivative substituted at C-6 by a trifluoromethyl group. It was tested whether flumedroxone had prophylactic value in migraine. No benefit was found in males, or in females with no history of menstrual exacerbation of migraine. In women whose migraine was worse around the time of menstruation flumedroxone resulted in statistically fewer headaches of less severity. With the dose used in this trial side-effects were frequent, the commonest being polymenorrhagia, which occurred in half the women of reproductive age.