古柯（英语：coca），在古柯科古柯属下四种植物的通称，原产于南美洲。在阿根廷，秘鲁，玻利维亚，乌拉圭，哥伦比亚等国家中，这是重要的经济作物，也是一种传统药草，在印加帝国文化中占有重要地位。古柯叶子中富含生物碱成份，其中包含咖啡因与古柯碱等。因为它是制作古柯碱的主要原料，因此其种植常是非法的。

古柯叶子中的古柯碱含量，只有0.25%至0.77%之间，含量很低。要经过数道提炼进程后，才能被纯化，制成古柯碱。一般嚼食古柯叶，或是饮用古柯茶，不会出现毒性反应，或造成生理上的问题。从1885年开始，可口可乐的配方中，就包含了古柯叶的抽取物。在大约1929年前后，可口可乐在加入古柯叶添加物之前，会先移除其中的古柯碱成份。

Coca is any of the four cultivated plants in the family Erythroxylaceae, native to western South America.

The plant is grown as a cash crop in Argentina, Bolivia, Colombia, Ecuador, and Peru, even in areas where its cultivation is unlawful. There are some reports that the plant is being cultivated in the south of Mexico as a cash crop and an alternative to smuggling its recreational product cocaine. It also plays a role in many traditional Andean cultures as well as the Sierra Nevada de Santa Marta (see Traditional uses). Coca is known throughout the world for its psychoactive alkaloid, cocaine. The alkaloid content of coca leaves is low, between 0.25% and 0.77%. This means that chewing the leaves or drinking coca tea does not produce the high (euphoria, megalomania, depression) people experience with cocaine. Coca leaf extract had been used in Coca-Cola products since 1885, with cocaine being completely eliminated from the products on or around 1929. Extraction of cocaine from coca requires several solvents and a chemical process known as an acid/base extraction, which can fairly easily extract the alkaloids from the plant.