There is no EU-harmonised maximum for melatonin in food supplements. The question is governed nationally, and member state positions range from a prescription-only classification to caps of several milligrams.
Portugal sets a national maximum of 1 mg per daily dose, in a 2016 opinion of the food and veterinary directorate on the boundary between medicines and food supplements. The directorate accepts notifications only for supplements at or below that figure and not intended for children. This is a borderline-product classification under food law, not a medicines or narcotics measure, and it is an agency opinion rather than a decree. Melatonin is not prescription-only in Portugal at supplement doses; an authorised 2 mg melatonin medicine exists separately and does not close the food route.
