Drug abuse is characterized by taking more than the recommended dose of prescription drugs such as barbiturates without medical supervision, or using government-controlled substances such as marijuana, cocaine, heroin, or other illegal substances. Legal substances, such as alcohol and nicotine, are also abused by many people. Abuse of drugs and other substances can lead to physical and psychological dependence.

Drug abuse can cause a wide variety of adverse physical reactions. Long-term drug use may damage the heart, liver, and brain. Drug abusers may suffer from malnutrition if they habitually forget to eat, cannot afford to buy food, or eat foods lacking the proper vitamins and minerals. Individuals who abuse injectable drugs risk contracting infections such as hepatitis and HIV from dirty needles or needles shared with other infected abusers. One of the most dangerous effects of illegal drug use is the potential for overdosing-that is, taking too large or too strong a dose for the body's systems to handle. A drug overdose may cause an individual to lose consciousness and to breathe inadequately. Without treatment, an individual may die from a drug overdose.

Drug addiction is marked by a compulsive craving for a substance. Successful treatment methods vary and include psychological counseling, or psychotherapy, and detoxification programs-medically supervised programs that gradually wean an individual from a drug over a period of days or weeks. Detoxification and psychotherapy are often used together.

The illegal use of drugs was once considered a problem unique to residents of poor, urban neighborhoods. Today, however, people from all economic levels, in both cities and suburbs, abuse drugs. Some people use drugs to relieve stress and to forget about their problems. Genetic factors may predispose other individuals to drug addiction. Environmental factors such as peer pressure, especially in young people, and the availability of drugs, also influence people to abuse drugs.