Severe headache involving attacks of pain, usually in one side of the head, nausea and vomiting. The pain is caused by narrowing of the blood vessels inside and outside the skull, followed by dilation, for reasons which are either hormonal, allergic or unknown. Migraine can occur in childhood, but usually begins at puberty; it often runs in families. Attacks usually happen during rest periods (weekend, holidays) or, in women, around the time of menstruation. Stress, smoking and alcohol also have an effect. Women often find that migraine attacks subside during pregnancy or after the menopause. Narrowing of the blood vessels causes the attack to begin with a tight feeling on one side of the head. At the same time the blood supply to one half of the brain is disturbed, causing symptoms in the other side of the body, such as tingling in the arm or leg. In rare cases temporary paralysis or aphasia occurs. After about 20 minutes the constricted veins dilate, and a pounding headache begins rapidly, finally leading to nausea and vomiting. A substantial number of patients experience only the headache, and not the symptoms associated with constriction of the blood vessels. A regular regime is essential if attacks are to be prevented. Medical treatment is directed mainly at preventing attacks, but there are drugs which can be given during them.