drug poisoning, toxic effects caused by an administered drug. Worldwide more than 9 million natural and synthetic chemicals have been identified; fewer than 3000 cause more than 95% of acidental and deliberate poisonings. Reaction to a drug caused by an allergic sensitivity is not considered drug poisoning. Virtually all drugs, especially in large doses or when taken over long periods of time, can initiate a toxic condition. Certain drugs used in combination, such as alcohol and barbiturates, result in an intensified alteration of physiological state that is frequently dangerous. Drugs that affect the nervous system often cause adverse reactions in high concentrations. Alcohol and other nervous system depressants, such as barbiturates and narcotics, taken in sufficiently large doses, can result in coma and convulsions. Excessively high doses of stimulants such as amphetamines result in blurred vision, spasms, heart irregularities, and respiratory failure. In addition, continued use of both stimulants and depressants can lead to addiction and tolerance for toxic doses. Overdosage of an analgesic like aspirin can result in acid-base disturbances, spontaneous bleeding, and convulsions. Virtually all drugs produce some side effects. For example, side reactions with barbiturates may include respiratory depression and skin rashes. Other drugs cause adverse reactions when taken over long periods of time. The antibiotic streptomycin taken over long periods can result in deafness, and continued use of aspirin and other salicylates can result in kidney damage and anemia. Some drugs only have toxic effects on sensitive individuals. Hallucinogenic drugs such as LSD can result in hyperexcitability, coma, and prolonged psychotic states and can cause major personality changes in some users. In susceptible persons even moderate doses of phenothiazine tranquilizers, which are used to calm psychotic patients, can cause such toxic effects as low blood pressure, uncontrollable muscle movements, and various pigmentation and blood cell disorders (see phenothiazine).