Depressant

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See also sedative.

A depressant, also known as a "downer," is a chemical agent that diminishes the function or activity of a specific part of the body. The term is used in particular with regard to the central nervous system (CNS). In that case these chemicals are known as neurotransmitters. Most depressants acting on the CNS do so by increasing the activity of a particular neurotransmitter known as gamma-aminobutyric acid (GABA), although other targets such as the NMDA receptor, mu-opioid receptor and CB1 cannabinoid receptor can also be important, depending on which drug is involved.

GABA's task is to calm the CNS and to promote sleep. Drugs that stimulate the production of this amino acid produce slowed brain activity and a drowsy or calm feeling, and so depressants are generally prescribed to relieve symptoms of anxiety or insomnia. Internal systems regulate the body's production of GABA, but when medication is taken to stimulate GABA production, it is possible to induce hazardously high levels, which can dangerously slow breathing and heart rates, and may result in death.

CNS depressants require a period of adaptation. Typically, initial side effects include slurred speech, dizziness, and loss of coordination, in many respects similar to the effects of alcohol (which is itself a CNS depressant).

The most commonly used depressants generally fall into two classes: barbiturates and benzodiazepines, but also include alcohol, narcotics (opiate derivatives) and sedative-hypnotics, as well as tranquilizers (such as Ketamine and PCP).

Barbiturates are effective in relieving the conditions they are designed to address; they are also readily abused, and when, in the late 1960s, it became clear that the social cost of barbiturates was beginning to outweigh the medical benefit, a serious search began for a replacement drug. (See Methaqualone) Most people still using barbiturates today do so in the prevention of seizures.

Benzodiazepines mediate the same symptoms as barbiturates, but without the same degree of toxic hazard. This is not to say they are not without their own risks; where barbiturates pose a greater "front-end" risk in that overdose or drug/alcohol interactions may result in fatality, benzodiazepines pose a greater "back-end" risk in the possibility of addiction and serious physical and psychological withdrawal symptoms. Even so, any attempt to consume alcohol while using barbiturates, or to attempt to stop benzodiazepine use "cold turkey" can be extremely dangerous and may result in death.