Symptoms of mild cinchonism (which may occur from standard therapeutic doses of quinine) include flushed and sweaty skin, tinnitus, blurred vision, impaired hearing, confusion, reversible high-frequency hearing loss, headache, abdominal pain, rashes, lichenoid photosensitivity [1], vertigo, dizziness, dysphoria (feeling uneasy), nausea and vomiting, and diarrhea.

Large doses of quinine may lead to severe symptoms of cinchonism: skin rashes, deafness, somnolence, diminished visual acuity or blindness, anaphylactoid shock, and disturbances in cardiac rhythm or conduction, death from cardiotoxicity.

Patients treated with quinine may also suffer from hypoglycemia (especially if administered intravenously) and hypotension (low blood pressure). In very high doses (higher than those used to treat malaria) during the first trimester of pregnancy quinine may act as an abortifacient, or cause birth defects, especially deafness.

Most symptoms of cinchonism (except in severe cases) are reversible and disappear once quinine is withdrawn.

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