depressant

Meaning: Depressants slow neural activity. The classic group is alcohol, barbiturates and benzodiazepines, which largely enhance GABA signaling, so neurons are less likely to fire. Opioids such as heroin and morphine also sedate and are sometimes grouped here, but many texts treat them as a separate class because they act on endorphin (opioid) receptors. Low doses reduce anxiety and inhibition. Higher doses impair coordination, judgment and memory and can slow breathing. Repeated use can lead to tolerance, dependence and withdrawal.

On the MCAT: Expect to classify a drug as a depressant, stimulant, opioid or hallucinogen. You may be asked to predict what a GABA-enhancing drug does to a neuron (more inhibition, so less firing). You may also be asked why stopping after heavy use causes rebound excitability, such as anxiety and agitation, as the brain's adaptation is left unopposed. Combining depressants, such as alcohol with barbiturates or benzodiazepines, strengthens their effects beyond simple addition and can dangerously suppress breathing.

Common confusion: A depressant is not a drug that causes depression, the mood disorder. It lowers nervous system activity. Alcohol can look stimulating at first, but this happens because it suppresses inhibitory control, not because it excites neurons directly.