Coca (Erythroxylum coca) is a native of the Andes Mountain. Cocaine is its active alkaloid and for centuries, the natives of Peru and Bolivia chew the leaves for its stimulating effects. Sherlock Holmes, the fictional detective, is a chronic cocaine user who liked to keep his wits occupied in between cases. Coca-Cola invented by John Pemberton in 1868 contained extracts from coca leaves and was marketed as a stimulant and a remedy for headache. Cocaine was later removed from the drink in 1906. The pupils dilate in response to its use and serves as a useful sign in suspected users. Cocaine also numbs the eye when applied directly to the eye. This property allows its used as local anaesethsia in eye surgery during the 19th and early 20th century. However, it fell out of favour because of its stimulatory effects on the patients and toxic effects to the eyes.

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