Overall, melatonin supplementation is relatively safe. First, melatonin toxicity is very low. Studies testing up to 240 mg[1] and 500 mg[2] taken orally do not report any toxic effects. Second, tolerance does not seem to be an issue. A study examining the continued administration of melatonin over 6–12 months did not find any evidence of tolerance.[3] Third, there is currently no evidence to support addiction or withdrawal symptoms. However, doses higher than 2 mg have not been sufficiently studied over the long term. Lastly, if you’re worried about the potential testosterone-lowering effect of melatonin, rest assured, there is currently no conclusive evidence to support this claim.
References
- ^F Waldhauser, H R Lieberman, H J Lynch, M Waldhauser, K Herkner, H Frisch, H Vierhapper, W Waldhäusl, M Schemper, R J WurtmanA pharmacological dose of melatonin increases PRL levels in males without altering those of GH, LH, FSH, TSH, testosterone or cortisolNeuroendocrinology.(1987 Aug)
- ^R Valcavi, C Dieguez, C Azzarito, C A Edwards, C Dotti, M D Page, I Portioli, M F ScanlonEffect of oral administration of melatonin on GH responses to GRF 1-44 in normal subjectsClin Endocrinol (Oxf).(1987 Apr)
- ^Patrick Lemoine, Doron Garfinkel, Moshe Laudon, Tali Nir, Nava ZisapelProlonged-release melatonin for insomnia - an open-label long-term study of efficacy, safety, and withdrawalTher Clin Risk Manag.(2011)