They first affect those areas of the brain that control a person's conscious, voluntary actions. As dosage increases, depressants begin to affect the parts of the brain controlling the body's automatic, unconscious processes, such as heartbeat and respiration.
Alcohol is the most familiar, and most widely abused depressant.
With some exceptions, all depressants affect people in much the same way as does alcohol. Most depressant users ingest these drugs orally. However, a few abusers will inject their drugs intravenously. The injection paraphernalia used by barbiturate abusers are similar to those used by heroin addicts, although a wider gauge hypodermic needle is used, because the barbiturate solution is thicker than the heroin solution. The injection sites on the skin of a barbiturate abuser exhibit large swellings, and may develop ulceration's resembling cigarette burns.