Towards the end of the 19th century the medical profession began to use the word addiction as both an explanation for, and diagnosis of, excessive drug use. One consequence of this change in attitude is the notion that the addict is not in control of their behaviour, that they require treatment rather than punishment. One problem with the disease model is that it not clear how one catches this disease. The presence of withdrawal symptoms led to the idea that the avoidance of withdrawal symptoms was the reason people continued to self-administer drugs. After repeated exposure to certain drugs, withdrawal symptoms appear if the drug is discontinued.
Withdrawal symptoms are compensatory reactions that oppose the primary effects of the drug.
Therefore they are the opposite of the effects of the drug. Concentrating on the role of physical withdrawal effects at the expense of other psychological factors led to the failure to recognize the addictive properties of cocaine. It is also important to emphasize that reduction in withdrawal symptoms does not explain why people take drugs in the first place. Negative reinforcement may account for initial drug taking in some situations. However the most likely reason for drug taking involves positive reinforcement.