Tolerance, Dependence and Addiction

Key points

• • Tolerance is when repeated use of a drug makes it less effective, so a larger amount is needed to get the same effect.
• • Tolerance can arise because the body breaks the drug down faster or because the target becomes less responsive to it.
• • Physical dependence is when the body has adapted to the drug, so stopping it suddenly causes a withdrawal reaction, often the opposite of the drug's effect.
• • Psychological dependence is a strong craving and drive to keep taking the drug for its pleasant effect or to avoid feeling bad.
• • Addiction (now often called substance use disorder) is compulsive drug-seeking and use despite harm; it is distinct from physical dependence and involves the brain's reward pathways.
• • Tachyphylaxis is a special, rapid form of tolerance that develops within minutes to hours of repeated use.