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A depressant, or central depressant, is a drug or endogenous compound that lowers or depresses arousal levels and reduces excitability. Depressants are also occasionally referred to as "downers" as they lower the level of arousal when taken. Stimulants or "uppers" increase mental and/or physical function are the functional opposites of depressants.
Depressants are widely used throughout the world as prescription medicines and as illicit substances. When these are used, effects often include anxiolysis, pain relief, sedation or somnolence, and cognitive/memory impairment, as well as in some instances euphoria, dissociation, muscle relaxation, lowered blood pressure or heart rate, respiratory depression, and anticonvulsant effects, and even complete anesthesia or death at high doses.
Depressants exert their effects through a number of different pharmacological mechanisms, the most prominent of which include facilitation of GABA or opioid activity, and inhibition of glutamatergic or catecholaminergic activity.
Depressants are used medicinally to relieve the following symptoms:
They are also used recreationally for the following purposes:
- To temporarily boost mood or induce euphoria
- To reduce social anxiety and improve sociability
Barbiturates are effective in relieving the conditions that they are designed to address. They are also commonly misused, physically addictive, and have serious potential for overdose. When, in the late 1950s, it became clear that the social cost of barbiturates was beginning to outweigh the medical benefits, a serious search began for a replacement drug. Most people still using barbiturates today do so in the prevention of seizures or in mild form for relief from the symptoms of migraines.
Although Cannabis or Marijuana is often considered either in its own unique category or as a mild psychedelic, the drug, notably the chemical compound Cannabidiol in it, still does nevertheless have many depressant effects such as muscle relaxation, sedation, decreased alertness, and tiredness.
- Alpha and beta blockers (Carvedilol, Propanolol, atenolol, etc.)
- Anticholinergics (Atropine, hyoscyamine, scopolamine, etc.)
- Anticonvulsants (Valproic acid, carbamazepine, lamotrigine, etc.)
- Antihistamines (Diphenhydramine, doxylamine, promethazine, etc.)
- Antipsychotics (Haloperidol, chlorpromazine, clozapine, etc.)
- Dissociatives (Dextromethorphan, ketamine, phencyclidine, nitrous oxide, etc.)
- Hypnotics (Zolpidem, zopiclone, chloral hydrate, chloroform, etc.)
- Muscle relaxants (Baclofen, carisoprodol, cyclobenzaprine, etc.)
- Sedatives (Gamma-hydroxybutyrate, etc.)
Combining multiple depressants can be very dangerous because the central nervous system's depressive properties has been proposed to increase exponentially instead of linearly. This characteristic makes depressants a common choice for deliberate overdoses in the case of suicide. The use of alcohol or benzodiazepines along with the usual dose of heroin is often the cause of overdose deaths in opiate addicts.
See also 
- Princeton WordNet http://wordnetweb.princeton.edu/perl/webwn?s=depressant
- Painfully Obvious - A Community Resource
- Fact sheets and Harm Reduction Strategies About Depressants and Other Recreational Drugs
- U.S. Department of Human and Health Services: Drug Categories for Substances of Abuse
- About Psychotropic Medications: Quick Reference to Medications Used in Mental Health