ABSTRACT
Psychoactive drugs have two basic uses: to alter mood and states of consciousness, and to treat psychopathology. In order for a drug to have an effect on behaviour, it must come into contact with the appropriate neurons in the brain. This can be accomplished in numerous ways, and the decision about the route of administration is based on a combination of factors including convenience, effects of the drug on local tissue, solubility of the drug, ionic characteristics of the drug, size of the drug molecule, and vulnerability of the drug to metabolism. One of the most elegant experiments in the history of pharmacology was performed in the mid-nineteenth century by a French physiologist, Claude Bernard. Explorers had brought back curare, a compound that native South Americans used as a poison on their blowgun darts to paralyse large mammals. Drugs that are classified as central nervous system depressants appear to act on two major neurotransmitter systems.
