From Longman Dictionary of Contemporary Englishmelatoninmel‧a‧to‧nin /ˌmeləˈtəʊnɪn $ -ˈtoʊ-/ noun [uncountable] a hormone that is sometimes used as a drug to help you sleep
Examples from the Corpus
melatonin• The results raise an interesting problem for people studying other effects of melatonin.• A synthetic form of melatonin can be bought over-the-counter at health food stores and many pharmacies.• Daily injections of melatonin given at 3.30 each afternoon, entrained the rats to a 24 hour cycle.• Perhaps melatonin would help him get a little rest.• When the sun goes down, the eyes cue the gland to start pumping melatonin.• There may be uncertainties surrounding melatonin, but it is clearly the dose of the moment.• The rat does not immediately adjust its daily rhythm to the melatonin.• Starlings, which are active during the day, lock on to melatonin when it coincides with the end of their activity.Origin melatonin (1900-2000) Greek melas “black” + English serotonin 