Drug tolerance

Drug tolerance is a pharmacology concept where a subject's reaction to a specific drug and concentration of the drug is reduced followed repeated use, requiring an increase in concentration to achieve the desired effect.

The following are characteristics of drug tolerance: it is reversible, the rate depends on the particular drug, dosage and frequency of use, differential development occurs for different effects of the same drug.

Tachyphylaxis

Tachyphylaxis is a sudden onset drug tolerance which is not dose dependent.

Pharmacodynamic tolerance

Pharmacodynamic tolerance occurs when the cellular response to a substance is reduced with repeated use. This may be caused by a reduced receptor response to receptor agonists (receptor desensitization), a reduction in receptor density (usually associated with receptor agonists), or other mechanisms leading to changes in action potential firing rate. Pharmacodynamic tolerance to a receptor antagonist involves the reverse, i.e., increased receptor firing rate, an increase in receptor density, or other mechanisms.