Drugs that lower neurotransmission levels, reducing brain activity
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Depressants, also known as central nervous system depressants, or colloquially known as "downers", are a class of psychoactive drugs characterised by decreasing neurotransmission levels, decreasing the electrical activity of brain cells, or reducing arousal or stimulation in various areas of the brain. Commonly used depressants include alcohol, opioids, and benzodiazepines. Some specific depressants influence mood, either positively (e.g., opioids) or negatively (e.g., alcohol), but depressants often have no clear impact on mood (e.g., most anticonvulsants). 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.
Depressants are closely related to sedatives as a category of drugs, with significant overlap. The terms may sometimes be used interchangeably or may be used in somewhat different contexts. Nearly all commonly used depressants are addictive, and use of them carries the risk of death from respiratory depression, especially in opioids.
Depressants are widely used throughout the world as prescription medicines and illicit substances. Alcohol is a very prominent depressant. When depressants are used, effects often include ataxia, anxiolysis, pain relief, sedation or somnolence, cognitive or memory impairment, as well as, in some instances, euphoria, dissociation, muscle relaxation, lowered blood pressure or heart rate, respiratory depression, and anticonvulsant effects. Depressants sometimes also act to produce anesthesia. Other depressants can include drugs like benzodiazepines (e.g., alprazolam) and a number of opioids. Gabapentinoids like gabapentin and pregabalin are depressants and have anticonvulsant and anxiolytic effects. Most anticonvulsants, like lamotrigine and phenytoin, are depressants. Carbamates, such as meprobamate, are depressants that are similar to barbiturates. Anesthetics are generally depressants; examples include ketamine and propofol.
Depressants exert their effects through a number of different pharmacological mechanisms, the most prominent of which include facilitation of GABA and inhibition of glutamatergic or monoaminergic activity. Other examples are chemicals that modify the electrical signaling inside the body, the most prominent of which are bromides and channel blockers.