Dutch and US researchers have concluded that a low dose of the hormone melatonin may help lower blood pressure. In a small study of 16 middle-aged men with untreated hypertension, the researchers administered 2.5 mg of melatonin 1 hour before bed each night for 3 weeks. Also, the patients took a placebo for 3 weeks.
The findings indicated that participants who received nightly melatonin supplements lowered their nighttime systolic blood pressure by ~6 mm Hg on average and their diastolic reading by ~4 mm Hg. No change was seen from taking 1 dose of melatonin, the researchers noted in Hypertension (February 2004).