A group of physiologic consequences that occur when chronic drug treatment is terminated or an antagonist is administered. Typically, the withdrawal syndrome has characteristics that are opposite in nature to the acute effects of the chronically administered drug. In most cases, the longer the drug is administered and the higher the dose, the more intense the withdrawal syndrome. Withdrawal is believed to be a result of the removal of the drug from its site of action (e.g., receptor). The more rapid the removal of the drug from its site of action, the more rapid the onset of withdrawal and the more severe the syndrome. As such, drugs with rapid elimination kinetics often have intense, but shorter lasting withdrawal syndrome. Similarly, the longer the elimination kinetics, the less intense, but longer lasting the withdrawal syndrome. In cases where a withdrawal syndrome occurs following administration of a drug that rapidly removes the chronic drug from its site of action, the syndrome can be explosive and particularly unpleasant.