Depressants are drugs that reduce neural activity and slow body functions. They calm the nervous system, produce drowsiness, and in higher doses can impair coordination, judgment, and breathing.

Alcohol is the most widely used depressant. It enhances the effects of the inhibitory neurotransmitter GABA and reduces the activity of glutamate, producing relaxation at low doses and sedation, memory blackouts, and respiratory depression at high doses. Barbiturates and benzodiazepines act on the same GABA system and are prescribed for anxiety and insomnia, yet they carry risks of dependence and dangerous interactions with alcohol. Opioids such as morphine and heroin also depress neural activity, primarily through pain pathways, and can slow breathing to life-threatening levels.

Tolerance develops with repeated use, so larger doses are needed for the same effect. Withdrawal can be severe and, in the case of alcohol and barbiturates, medically dangerous. Overdose remains a leading cause of drug-related death, especially when depressants are combined.

Depressants quiet the nervous system. In excess they can quiet it permanently.