Coca is a plant native to north-western South America, and has for centuries played a significant role in traditional Andean culture. There are two species, Erythroxylum coca , and E. novogranatense , each existing in two varieties. The plant, which resembles a blackthorn bush, is well known as a source of cocaine, and grows to a height of two to three metres. The plants are cultivated mainly on the lower slopes of the eastern side of the Andes.
Coca leaves have been used for centuries as a stimulant. Pre-Incan Indians used the leaves to relieve altitude sickness, caused by hypoxia, as well as for relief of hunger and fatigue. Since ancient times, its leaves have been an important trade commodity between the lowlands, where it is chiefly cultivated, and the higher altitudes, where it is widely consumed. Traces of coca have been found in archaeological evidence dating back 6,000 years, with mummies discovered buried with a supply of coca leaves, along with pottery decorated with depictions of figures displaying the characteristic cheek bulge of the coca chewer.
In 1961, the United Nations Convention on Narcotic Drugs listed coca leaf as a Schedule 1 substance, making its use illegal. However, Peru and Bolivia, in particular, cited a clause which stated that measures to eradicate illicit cultivation should take into account traditional cultural use, where historical evidence exists, and coca leaves remain legal in these countries and their use is widespread.
The leaves contain alkaloids that are a source of cocaine base, with the principal psychoactive ingredient being benzoylmethylecgonine. The leaves are traditionally either chewed, or brewed in a tea known as “Mate de Coca”. The traditional method of chewing is known as “acullico”, and consists of keeping a saliva-soaked ball of coca leaves in the mouth, together with an alkaline substance, commonly bicarbonate of soda, that facilitates the extraction of alkaloids from the leaves. Absorption of the coca alkaloids from tea is slower and less complete than chewing. The coca leaf, when consumed in its natural form, does not induce a physiological or psychological dependence, nor does abstinence after long-term use produce symptoms typical to substance addiction, and coca leaves have been employed in some parts of South America as a method to help wean recovering cocaine addicts off the drug.
Research  carried out in Bolivia on the effects on physical performance of chewing coca leaves suggested that they block the glycolytic pathway of glucose oxidation at the pyruvate dehydrogenase level, resulting in a switch to energy production from fatty acids, a more efficient source of energy during sustained periods of low-level exercise, providing users with energy to function at a sustained level over long periods of time. However, the amount of cocaine absorbed through chewing is very small, and is thought unlikely to be responsible for any physiological benefit, and it has been suggested that the effect may in fact be exerted by flavonoids contained within the leaves, and further research is being carried out into these compounds.
1) Indian J Clin Biochem. Jul 2010; 25(3): 311–314, published online Aug 25, 2010. doi: 10.1007/s12291-010-0059-1