Two-fold nature

Drug rehabilitation tends to address a stated twofold nature of drug dependency: physical and psychological dependency. Physical dependency involves a detoxification process to cope with withdrawal symptoms from regular use of a drug. With regular use of many drugs, legal or otherwise, the brain gradually adapts to the presence of the drug so the desired effect is minimal. Apparently normal functioning of the user may be observed, despite being under the influence of the drug. This is how physical tolerance develops to drugs such as heroin, amphetamines, cocaine, nicotine or alcohol. It also explains why more of the drug is needed to get the same effect with regular use. The abrupt cessation of taking a drug can lead to withdrawal symptoms where the body may take weeks or months (depending on the drug involved) to return to normal.