Physical dependence
Physical dependence is a physiological adaptation to a substance that can cause withdrawal symptoms when use is reduced or stopped.
Neuroadaptation: A lasting change in nervous-system function caused by repeated experience or exposure. Repeated substance exposure can adapt neural systems, producing dependence and withdrawal.
Psychological dependence: Reliance on a substance for its emotional or mental effects, including relief, pleasure, or coping. Physical dependence concerns physiological adaptation; psychological reliance concerns perceived emotional or mental need.
Opioid withdrawal: A syndrome following reduction or cessation of opioids after physiological adaptation. Opioids provide a common, clinically significant example of physical dependence.
Homeostasis: The regulation of internal conditions within ranges compatible with normal functioning. Dependence develops as regulatory systems compensate for a substance that repeatedly alters their activity.
Individual variability in drug response: Differences among people in how they respond to the same drug exposure. Dose, duration, biology, and circumstances help explain why dependence and withdrawal differ between people.
Tolerance: A reduced response to a substance after repeated exposure, often leading to larger doses for the same effect. Tolerance can develop alongside physical dependence, though one does not always imply the other.
Substance use disorder: A clinical pattern of substance use causing significant impairment or distress. Physical dependence may occur within a substance use disorder but is not itself the diagnosis.
Alcohol withdrawal syndrome: A potentially dangerous set of symptoms after stopping or sharply reducing prolonged heavy alcohol use. Alcohol dependence can produce severe withdrawal, including seizures and delirium.
Pharmacodynamics: The study of how drugs affect the body and how those effects relate to dose. Drug effects on bodily targets initiate adaptations that can underlie dependence.
Protracted withdrawal: Symptoms that persist or emerge after the acute withdrawal phase has ended. The causes, duration, and best treatment of prolonged symptoms remain debated for some substances.