Psychoactive drugs are chemical substances that alter mood, behavior, perception, or mental functioning. Throughout history, many cultures have found ways to alter consciousness through the ingestion of substances. In current professional practice, psychoactive substances known as psychotropic drugs have been developed to treat patients with severe mental illness.
Psychoactive substances exert their effects by modifying biochemical or physiological processes in the brain. The message system of nerve cells, or neurons, relies on both electrical and chemical transmission. Neurons rarely touch each other; the microscopic gap between one neuron and the next, called the synapse, is bridged by chemicals called neuroregulators, or neurotransmitters. Psychoactive drugs act by altering neurotransmitter function. The drugs can be divided into six major pharmacological classes based on their desired behavioral or psychological effect: alcohol, sedative-hypnotics, narcotic analgesics, stimulant-euphoriants, hallucinogens, and psychotropic agents.
Alcohol has always been the most widely used psychoactive substance. In most countries it is the only psychoactive drug legally available without prescription.
Pleasant relaxation is commonly the desired effect, but intoxication impairs judgment and motor performance. When used chronically, alcohol can be toxic to liver and brain cells and can be physiologically addicting, producing dangerous withdrawal syndromes.
Sedative-hypnotics, such as the barbiturates and diazepam (widely known under the brand name Valium), include brain depressants, which are used medically to help people sleep, and antianxiety agents, which are used to calm people without inducing sleep. Sedative-hypnotics are used illegally to produce relaxation, tranquillity, and euphoria. Overdoses of sedative-hypnotics can be fatal; all can be physiologically addicting, and some can cause a life-threatening withdrawal syndrome.
Narcotic analgesics--opiates such as morphine and heroin--are prescribed to produce analgesia. Because the relief of pain is one of the primary tasks of medical treatment, opiates have been among the most important and valuable drugs in medicine. Illegal...