Melatonin supplements, often taken for difficulty in sleeping, appear
to be safe when used over short periods at high doses, according to a report
by the Agency for Healthcare Research and Quality (http://www.ahrq.gov/clinic/evrptpdfs.htm#melatonin). However, safety of the supplements when used over months or years
is not clear.
Hampton T. Melatonin Supplements. JAMA. 2005;293(8):921. doi:10.1001/jama.293.8.921-b