Unisom (diphenhydramine or doxylamine) is an antihistamine used as an over-the-counter sleep aid. Antihistamines often cause drowsiness and sedation and can be used to help with difficult falling asleep. Unisom capsules and chewable tablets have diphenhydramine as an active ingredient, and the tablets have doxylamine; both are available as generic antihistamine sleep aids.

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