Many questions regarding the safety and effectiveness of melatonin remain to be answered. The first is the safety of the source. The safety of any animal product is cause for concern.
Appropriate dosage remains an unanswered question.
Some feel that less than 0.5 mg is an appropriate dose, but the tablets sold generally contain 2 to 3 mg. Adverse effects now known including memory loss, chronic grogginess, nausea, headaches, fatigue, and possibly infertility. Melatonin may reduce follicle-stimulating hormone levels. Pregnant mice given melatonin had a high rate of embryo death. There are steps one can take to encourage natural melatonin production, decreasing the risk of adverse effects.