Sedatives are drugs that produce sleep or drowsiness by depressing central nervous system (CNS) function. There are a number of drugs and drug classes that can produce drowsiness, but for which sedation is not the primary effect or use. Drugs that are used therapeutically as sedatives generally fall into one of three categories: positive GABAA receptor modulators (e.g., barbiturates, benzodiazepines); antihistamines (e.g., diphenhydramine, trade name Benadryl; doxylamine, trade name Unisom); and melatonin or melatonin receptor agonists (e.g., ramelteon, trade name Rozerem).