Regular users of drugs develop tolerance, a need to take larger doses to get the same initial effect. They may respond by combining drugs, frequently with devastating results. Certain drugs, such as opiates, barbiturates, alcohol, and nicotine, create physical dependence. With prolonged use, these drugs become part of the body chemistry. When a regular user stops taking the drug, the body experiences the physiological trauma known as withdrawal.
Psychological dependence occurs when taking drugs becomes the center of the user's life.
Psychological dependence on drugs can destroy ties to family and friends, as well as cause the user to abandon outside interests, values, and goals. The user goes from taking drugs to feel good, to taking them to keep from feeling bad. Over time, drug use itself heightens the bad feelings and can leave the user suicidal. Drugs can remain in the body long after use has stopped. The extent to which a drug is retained in the body depends on the drug's chemical composition.