withdrawal syndrome

A withdrawal syndrome is the cluster of symptoms that appears when a drug the body has grown used to is suddenly stopped or sharply reduced. The body had adapted to the drug's constant presence; remove it abruptly and that adaptation, now unopposed, rebounds and causes distress.

The underlying cause is physical dependence. With repeated exposure, the nervous system rebalances itself to counter the drug — for example, by down-regulating receptors a drug stimulates, or up-regulating systems the drug suppresses. While the drug is present this counter-adjustment is masked; once the drug disappears, the now-unbalanced system swings the opposite way, often producing symptoms that are the mirror image of the drug's effects.

The picture is drug-specific. Opioid withdrawal brings anxiety, sweating, cramps, and diarrhoea; abrupt stoppage of alcohol or benzodiazepines can cause dangerous seizures and delirium; suddenly stopping a beta-blocker can trigger rebound hypertension and angina. Some withdrawals are merely miserable, while others are genuinely life-threatening, which is a crucial distinction.

Importantly, physical dependence and withdrawal are not the same as addiction: a patient can become physically dependent on a properly prescribed drug without any compulsive drug-seeking behaviour. This is why many such drugs are tapered gradually rather than stopped at once — giving the adapted body time to readjust safely.