The depressants include several classes of pharmaceutical drugs, mainly developed and marketed as sleep aids, tranquilizers, anesthetic agents, muscle relaxers, and anticonvulsants.

Inappropriate prescribing and illegal diversion are the two main sources of these drugs on the street, although some “pirated” versions imported from illegal labs are also available.

The two most common varieties of depressants we en-counter are the barbiturates, such as Seconal and Tuinal, and the benzodiazepines, such as Valium and Xanax. Other less common and older depressants include such compounds as Quaalude (no longer legally available in the United States), chloral hydrate (the active ingredient in a Mickey Finn), paraldehyde (widely used in the past to treat severe alcohol withdrawal), and obsolete tranquilizers such as Placidyl, Miltown, and Equanil.

Barbiturates
The barbiturates have been around for quite a while, and are used primarily as general anesthetics and anticonvulsants.

In the past they were used as tranquilizers and sleeping pills, but this practice has diminished, for safety reasons, since the benzodiazepines became available.

The barbiturates act in a dose-related fashion. At low doses they produce mild sedation. With increasing doses, this effect progresses from sleep to anesthesia to respiratory depression to death. These drugs also have a low therapeutic index, meaning that the dose required for the desired effect - sedation, sleep or anesthesia - is very close to the toxic dose.

People suffering from barbiturate overdose, an extremely dangerous situation, were once commonly seen in emergency rooms. Often these overdoses were accidental. The user, having begun to develop tolerance to the drug’s sedative effects, would repeat the dose. (This was alleged to have been the cause of Marilyn Monroe’s death.)

Barbiturates cause addiction in two ways. A person can develop a physical dependence on the effects of the barbiturate as tolerance develops to the sedative effects. Stopping these drugs abruptly will lead to symptoms of withdrawal.

Withdrawal from barbiturates is very dangerous, involving agitation, anxiety, muscle cramps, seizures, delirium, and possibly death. Repetitive use of barbiturates to avoid the symptoms of withdrawal contributes to the addiction. But barbiturates also interact with the pleasure center of the brain to produce the same reinforcing response caused by other drugs of addiction.