GC: n

S: GDT; NAVARRO p. 1011; http://www.drugabuse.gov/publications/teaching-packets/neurobiology-drug-addiction/section-iii-action-heroin-morphine/6-definition-tolerance (last access: 5 September 2014).

N: 1. tolerance (n.): early 15c., “endurance, fortitude” (in the face of pain, hardship, etc.), from Old French tolerance (14c.), from Latin tolerantia “a bearing, supporting, endurance,” from tolerans, present participle of tolerare “to bear, endure, tolerate” (see toleration). Of individuals, with the sense “tendency to be free from bigotry or severity in judging other,” from 1765. Meaning “allowable amount of variation” dates from 1868; and physiological sense of “ability to take large doses” first recorded 1875.
2. Tolerance and Resistance to Drugs: Tolerance is a person’s diminished response to a drug, which occurs when the drug is used repeatedly and the body adapts to the continued presence of the drug. Resistance refers to the ability of microorganisms or cancer cells to withstand the effects of a drug usually effective against them.
3. A person may develop tolerance to a drug when the drug is used repeatedly. For instance, when morphine
or alcohol is used for a long time, larger and larger doses must be taken to produce the same effect. Usually, tolerance develops because metabolism of the drug speeds up (often because the liver enzymes involved in metabolizing drugs become more active) and because the number of sites (cell receptors) that the drug attaches to or the strength of the bond (affinity) between the receptor and drug decreases (see Receptors on Cells).
4. Tolerance is not the same as dependence or addiction. Dependence (see Drug Dependence), which may be physical or psychologic, refers to a strong desire to experience the effects of the drug. In physical dependence, the person may experience symptoms of withdrawal when the drug is stopped. Addiction is compulsive use and overwhelming involvement with a drug (see Drug Addiction).

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=tolerance&searchmode=none (last access: 5 September 2014). 2, 3 & 4. http://www.merckmanuals.com/home/drugs/factors_affecting_response_to_drugs/tolerance_and_resistance_to_drugs.html (last access: 5 September 2014)

SYN: drug tolerance

S: GDT; TERMIUMPLUS.

CR: tolerability