Based on the available data, it appears that short-term use of melatonin in a daily amount of 10 mg or less does not raise concern of harm for healthy adults who are not taking concurrent medications or other dietary supplements. The basis for each of these qualifications is explained below. Long-term use of melatonin increases the level of concern because use for periods longer than a few weeks has not been documented except in a small number of subjects or for therapeutic uses (e.g., entrainment of blind individuals). Use of melatonin in amounts above 10 mg per day increases the level of concern because there are only a few clinical studies using these amounts and, in some, serious adverse effects were observed. Use of melatonin in populations other than healthy adults increases the level of concern based in part on the observation that serious adverse effects reported at 10 mg or less of melatonin per day generally occurred in humans with preexisting medical or psychological conditions that may have contributed to the ill effects. Specifically, concern of harm exists for individuals with one or more of the following: (1) past or current depression; (2) cardiovascular problems; (3) seizure disorders; (4) immune system disorders; (5) chronic liver disease; (6) chronic kidney disease; (7) predisposition to headaches; especially migraine headaches; and (8) concurrent use of anticonvulsant, sedative, hypnotic, or psychotropic medications. One exception to the lack of concern of harm in healthy adults is that women attempting to become pregnant should be aware that melatonin may affect reproductive function, including possible effects on hormone levels (Forsling et al., 1999; Ninomiya et al., 2001; Okatani and Sagara, 1993; Pawlikowski et al., 2002). Use of melatonin by children cannot be recommended without supervision by a physician due to the lack of data available for individuals below the age of 18 years and possible effects on hormone levels (Forsling et al., 1999; Luboshitzky et al., 2002; Ninomiya et al., 2001; Okatani and Sagara, 1993; Pawlikowski et al., 2002; Valcavi et al., 1987).
Even among healthy adults, caution about use of melatonin should be considered for (1) individuals participating in functions that require alertness (e.g., operating a motor vehicle or machinery), (2) lactating women, and (3) individuals ingesting medications or other dietary supplements.
Uncertainty about potential for harm with the use of melatonin remains because of the following factors: