Colloquially known as "downers", depressants or CNS depressants are drugs that lower neurotransmission levels, decrease the electrical activity of brain cells, or reduce arousal or stimulation in various areas of the brain. Some specific depressants do influence mood, either positively or negatively, but depressants often have no clear impact on mood. In contrast, stimulants, or "uppers", increase mental alertness, making stimulants the opposite drug class from depressants. Antidepressants are defined by their effect on mood, not on general brain activity, so they form an orthogonal category of drugs.

अवसादक (Depressant) वे नारकोटिक औषधियाँ हैं जो न्यूरोट्रांसमिशन के स्तर को घाटाती हैं जिससे अवसाद बढ़ता है तथा कोई भी कार्य करने की क्षमता और उत्तेजना कम होती है।