A drug is any substance that, when absorbed into the body of a living organism, alters normal bodily function. In pharmacology, a drug is a chemical substance used in the treatment, cure, prevention, or diagnosis or used to otherwise enhance physical or mental well-being. Drugs may be prescribed for a limited duration, or on a regular basis for chronic disorders. Recreational drugs are chemical substances that affect the central nervous system, such as opioids or hallucinogens. They may be used for perceived beneficial effects on perception, consciousness, personality, and behavior. Some drugs can cause addiction and habituation. Many natural substances such as beers, wine, and some mushrooms, blur the line between food and drugs, as when ingested they affect the functioning of both mind and body.