There is no EU-harmonised rule 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.

Latvia governs food supplements by Cabinet Regulation No. 685, Prasības uztura bagātinātājiem, adopted on 1 December 2015 and published in Latvijas Vēstnesis No. 242 of 10 December 2015. A supplement may be placed on the Latvian market if it has been notified to the food and veterinary service and entered in the supplement register, and if it is presented as a food and supplied to the final consumer only pre-packaged. The regulation sets maximum permitted amounts only for vitamins and minerals; it names no maximum for melatonin, and no Latvian instrument names melatonin at all.

Melatonin also exists in Latvia as a registered medicine, but that does not foreclose the food supplement route, and melatonin supplements are notified, registered and openly sold.