From the United States National Institute of Health, Principles of Drug Addiction Treatment: A Research Based Guide – Why can’t drug addicts quit on their own?
Nearly all addicted individuals believe in the beginning that they can stop using drugs on their own, and most try to stop without treatment. However, most of these attempts result in failure to achieve long-term abstinence. Research has shown that long-term drug use results in significant changes in brain function that persist long after the individual stops using drugs. These drug-induced changes in brain function may have many behavioral consequences, including the compulsion to use drugs despite adverse consequences – the defining characteristic of addiction.
Long-term drug use results in significant changes in brain function that persist long after the individual stops using drugs.
Understanding that addiction has such an important biological component may help explain an individual’s difficulty in achieving and maintaining abstinence without treatment. Psychological stress from work or family problems, social cues (such as meeting individuals from one’s drug-using past), or the environment (such as encountering streets, objects, or even smells associated with drug use) can interact with biological factors to hinder attainment of sustained abstinence and make relapse more likely. Research studies indicate that even the most severely addicted individuals can participate actively in treatment and that active participation is essential to good outcomes.
Source: NIH Publication No. 00-4180 July 2000