Differential sensitivity to morphine challenge in migraine sufferers and headache-exempt subjects.

The effectiveness of a therapeutic dose of morphine in relieving migraine attacks was compared with placebo. Morphine was no more effective than placebo and provoked severe side effects. When low-dose morphine was administered to normal non-headache controls and migraineurs when headache-free, physical and psychologic reactions were induced only in migraineurs. On pupillometric study, only migraineurs had defective morphine-miosis. It is suggested that the observed clinical phenomena in response to morphine can be explained by differences in expression and sensitivity of some opioid receptor subtypes in migraine.