PIP: The currently recognized toxic effects of quinine in humans are identified and the problems of management of overdosage of quinine are discussed. Quinine, available therapeutically as sulphate or hydrochloride salts, also is widely used in tonic water, and there are several case reports of allergic reactions to the drug when a patient has consumed the drug in this way. Another unintentional source of poisoning is its use as an adulterant in heroin for "street" use. This appears to be a problem in the US. Quinine, termed a "general protoplasmic poison" is toxic to many bacteria, yeasts, and trypanosomes, as well as to malarial plasmodia. Quinine has local anesthetic action but also is an irritant. The irritant effects may be responsible in part for the nausea associated with its clinical use. In addition it has a mild antipyretic effect. Several features are common to both an acute single overdose in self-poisoning and accumulation of quinine during therapy for malaria: together they are termed cinchonism. Auditory symptoms, gastrointestinal disturbances, vasodilatation, sweating, and headache occur with moderately elevated plasma quinine concentration. As these rise, increasingly severe visual disturbances and then cardiac and neurologic features occur. Mild nausea may be the only symptom, but with large overdoses profuse vomiting, abdominal pain, and diarrhea may occur. These result from a combination of the local irritant effect of quinine on the gut and the central effects of quinine on the chemoreceptor trigger zone. Vasodilatation and sweating are well recognized, and tinnitus is common. Visual symptoms usually are delayed, and blindness may not be discovered for a day or more. Aspirin-sensitive patients, and others, may develop angioedema by nonimmunological mechanisms in response to drugs, and quinine has been reported to produce pseudo-allergic reactions in aspirin-sensitive patients. Quinine also can cause drug-induced thrombocytopenia and purpura. In patients suffering with malaria due to "Plasmodium falciparum," anemia and acute intravascular hemolysis with renal failure are recognized complications. There appears to be little evidence in the literature in support of the folk tradition of quinine as an inducer of abortion. Quinine is known to cause deterioration in patients with myasthenia gravis and erythema multiforme, to stimulate insulin release in patients receiving treatment for falicparum malaria, and to be responsible at times for ataxia following moderate overdosage. Clinically, quinine poisoning is observed in 3 situations: self-poisoning; accidentally; and following use of quinine in excessive doses in the hope of achieving abortion. Treatment courses are reviewed.