High Quality Content by WIKIPEDIA articles! Cinchonism or quinism is a pathological condition in humans caused by an overdose of quinine or its natural source, cinchona bark. Quinine is medically used to treat malaria. In much smaller amounts, quinine is an ingredient of tonic drinks, acting as a bittering agent. Cinchonism can occur from therapeutic doses of quinine, either from one or several large doses, or from small doses over a longer period of time, not from the amounts used in tonic drinks, but possibly from ingestion of tonic water as a beverage over a lengthy period of time. Quinidine (Class 1A anti-arrhythmic) can also cause cinchonism symptoms to develop with as little as a single dose.