Melatonin is a hormone that is made in the body's pineal gland. It is involved in the regulation of the body's circadian rhythm (sleep and wake cycles). Melatonin supplements are sometimes used to treat insomnia, jet lag, shift-work disorder (altered sleep cycles due to night-shift work), and nicotine withdrawal. In a recent study, researchers found that melatonin may have an effect on nocturnal (night time) blood pressure as well. It has been shown that some patients who take prescription drugs for high blood pressure do not experience the same drop in blood pressure during the night as do others. Patients who do not experience a night time drop in blood pressure are thought to be at a greater risk of heart attack. In the current study, nine women who were currently taking high blood pressure medications also took 3mg of melatonin 1 hour before bedtime for 3 weeks. Compared to the group of women who did not take melatonin, those who also took melatonin supplements had significantly lower nocturnal blood pressures.