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 the DGAV opinion Definição de fronteiras entre medicamentos e suplementos alimentares - Parecer melatonina, published 28 July 2016: os suplementos alimentares não devem ter teores de melatonina superiores a 1 mg (toma diária). DGAV 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 Portaria or Decreto-Lei. Melatonin is not prescription-only in Portugal at supplement doses; the authorised medicine Circadin 2 mg exists separately and does not close the food route.