Melatonin — Shabbat and Yom Tov

Is it permitted to take melatonin (a sleep supplement) on Shabbat and on Rosh Hashanah in the form of a flavored lozenge/candy? Also, is it permitted to take Ritalin (a medication) on Shabbat not for the purpose of regular functioning, but in order to study for an exam in a sacred-studies subject for girls?

Shalom u’vrachah 

It should be mixed before Shabbat / the festival into a drink or food — in such a way that it is not evident that one is eating something for medicinal purposes. 

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