Withdrawal is a constellation of aversive symptoms—ranging from anxiety, tremors (“the shakes”), and nausea to hallucinations and frank seizures—brought on by the sudden stoppage or dosage drop of long-term drug use. It is the clinical manifestation of abrupt cessation of a substance of abuse. Symptoms vary in severity and duration depending on the substance, how long it was used, how potent it is, its duration of action, and how quickly the drug is cleared from the body (its half-life), but all are caused by disruption in the brain’s accustomed pathways of nerve activity.
The longer a substance is used and the more potent it is, the more likely it is to produce withdrawal symptoms. The acute symptoms of withdrawal can last a week to 10 days, but the more psychological symptoms of withdrawal, such as anxiety or depression, can last for weeks or months.
Withdrawal, like addiction itself, reflects the capacity of the brain to adapt to experience. Addiction doesn’t develop overnight; over time, the repeated use of psychoactive drugs reprograms various circuits in the brain, and especially in its dopamine-rich reward center, so that they increasingly depend on the substance (dependence). When that substance is suddenly stopped, those nerve pathways are caught short. In the weeks and months after substance use is stopped, the brain rewires itself to essentially reverse the adaptations it made to the substance and return to normal, but that process takes time. In the short haul, fear of the unpleasantness of withdrawal often keeps people using a substance even when they want to stop.