Coca (Erythroxylum coca, Lam.) is a plant in the family Erythroxylaceae, native to northwestern South America. Under the older Cronquist system of classifying flowering plants, this was placed in an order Linales; more modern systems place it in the order Malpighiales.
The plant resembles a blackthorn bush, and grows to a height of 2-3 m. The branches are straight, and the leaves, which have a green tint, are thin, opaque, oval, more or less tapering at the extremities. A marked characteristic of the leaf is an areolated portion bounded by two longitudinal curved lines once on each side of the midrib, and more conspicuous on the under face of the leaf.
The flowers are small, and disposed in little clusters on short stalks; the corolla is composed of five yellowish-white petals, the anthers are heart-shaped, and the pistil consists of three carpels united to form a three-chambered ovary. The flowers are mature into red berries.
The leaves are sometimes eaten by the moth Eloria noyesi.
Coca is traditionally cultivated in the lower altitudes of the eastern slopes of the Andes. Since time immemorial, its leaves have been used as a stimulant by the indigenous people of Peru, Bolivia, and northern Argentina; it also has religious and symbolic significance. Since the 1980s, the cultivation of coca has become controversial because it is used for the manufacture of the drug cocaine, which is illegal in most countries.
Good samples of the dried leaves are uncurled, are of a deep green on the upper, and a grey-green on the lower surface, and have a strong tea-like odor; when chewed they produce a faint numbness in the mouth, and have a pleasant, pungent taste. Bad specimens have a camphoraceous smell and a brownish colour, and lack the pungent taste.
The seeds are sown in December and January in small plots (almacigas) sheltered from the sun, and the young plants when from 40-60 cm in height are placed in holes (aspi), or, if the ground is level, in furrows (uachos) in carefully weeded soil. The plants thrive best in hot, damp situations, such as the clearings of forests; but the leaves most preferred are obtained in drier localities, on the sides of hills. The leaves are gathered from plants varying in age from one and a half to upwards of forty years. They are considered ready for plucking when they break on being bent. The first and most abundant harvest is in March, after the rains; the second is at the end of June, the third in October or November. The green leaves (matu) are spread in thin layers on coarse woollen cloths and dried in the sun; they are then packed in sacks, which, in order to preserve the quality of the leaves, must be kept from damp.

Pharmological aspects
The pharmacologically active ingredient of coca is the alkaloid cocaine which is found in the amount of about 0.2% in fresh leaves. Besides cocaine, the coca leaf contains a number of other alkaloids, including Methylecgonine cinnamate, Benzoylecgonine, Truxilline, Hydroxytropacocaine, Tropacocaine, Ecgonine, Cuscohygrine, Dihydrocuscohygrine, Nicotine and Hygrine.
Traditional uses
In the Andes, the indigenous peoples have been chewing the leaves of the coca plant for millennia. They traditionally carried a woven pouch called a chuspa or huallqui in which they kept a day's supply of coca leaves, along with a small amount of ilucta or uipta, which is made from pulverized unslaked lime or from the ashes of the quinoa plant. A tiny quantity of ilucta is chewed together with the coca leaves; it softens their astringent flavor and activates the alkaloids.
The practice of chewing coca was most likely originally a simple matter of survival. The coca leaf contained many essential nutrients in addition to its more well-known mood-altering alkaloid. It is rich in protein and vitamins, and it grows in regions where other food sources are scarce. The perceived boost in energy and strength provided by the cocaine in coca leaves was also very functional in an area where oxygen is scarce and extensive walking is essential. The coca plant was so central to the worldview of the Yunga and Aymara tribes of South America that distance was often measured in units called "cocada", which signified the number of mouthfuls of coca that one would chew while walking from one point to another. In fact, the word "coca" itself most likely originally simply meant "plant".
Coca was also a vital part of the religious cosmology of the Andean tribes in the pre-Inca period as well as throughout the Inca Empire (Tahuantinsuyu). Coca was historically employed as an offering to the Sun, or to produce smoke at the great sacrifices; and the priests, it was believed, must chew it during the performance of religious ceremonies, otherwise the gods would not be propitiated. Coca is still held in superstitious veneration among the Peruvians, and is believed by the miners of Cerro de Pasco to soften the veins of ore, if masticated (chewed) and thrown upon them).
The activity of chewing coca is called chacchar or acullicar. Doing so usually causes users to feel a tingling and numbing sensation in their mouths, similar to receiving novocain during a dental procedure. Even today, chewing coca leaves is a common sight in indigenous communities across the central Andean region, particularly in places like the mountains of Bolivia, where the cultivation and consumption of coca is as much a part of the national culture as wine is to France or beer is to Germany. Bags of coca leaves are sold in local markets. Commercially manufactured coca teas are also available in most stores and supermarkets.
Industrial use
Coca is used industrially in the cosmetics and food industries. The Coca-Cola Company buys 115 tons of coca leaf from Peru and 105 tons from Bolivia per year, which it uses as an ingredient in its secret soft-drink formula. The cocaine itself does not end up in the drink nowadays, however. [1]
Legality
International
Article 26 of the Single Convention on Narcotic Drugs states:
1. If a Party permits the cultivation of the coca bush, it shall apply thereto and to coca leaves the system of controls as provided in article 23 respecting the control of the opium poppy, but as regards paragraph 2 (d) of that article, the requirements imposed on the Agency therein referred to shall be only to take physical possession of the crops as soon as possible after the end of the harvest.
2. The Parties shall so far as possible enforce the uprooting of all coca bushes which grow wild. They shall destroy the coca bushes if illegally cultivated.
The Article 23 controls referred to in paragraph 1 are rules requiring opium-, coca-, and cannabis-cultivating nations to designate an agency to regulate said cultivation and take physical possession of the crops as soon as possible after harvest. Article 27 states that "The Parties may permit the use of coca leaves for the preparation of a flavouring agent, which shall not contain any alkaloids, and, to the extent necessary for such use, may permit the production, import, export, trade in and possession of such leaves". This provision is designed to accomodate Coca-Cola and other producers of coca products. (Wikipedia)

Cultivation
Coca plants are small evergreen shrubs with reddish brown bark. They have many small branchlets with elliptical-obovate opposite leaves measuring 4-7 cm. in length and 3-4 cm. wide. The plants possess small yellowish-green flowers, which develop into red drupes. The leaves of the Colombian coca are smaller and less pointed at the end than Bolivian coca leaves (De Witt, 1967).
Andean natives grow coca from seed. The women collect the drupes when they are almost ripe. The drupes are placed in a basket and allowed to set until the fruit becomes soft. The pulp is then washed away and the seeds are allowed to dry in the sun.
The seeds are then placed in seed beds and germinate in approximately 24 days. When seedlings have four leaves a lattice covering is placed over them protecting them for a year.
When the young plants reach a height of 30-40 -cm. they are transplanted to prepared fields. This transplanting is done during the rainy season. At three years the plants may produce a small harvest of leaves. After the third year leaves are harvested, by the women, three or four times a year (Bastien, 1987). Yields may range from 1,500-2,000 lbs. of dry leaves/acre/year and planting are renewed every twenty years (Purseglove, 1977).
Pests that affect the coca plants range from weedy species that rob seedlings of soil nutrients and light to insect species such as the cuqi, an ant, which cuts roots and chews leaves, and ulo, a butterfly and its larva, which eat the plant. Another insect species known as mounga burrows into the trunk and destroys the plant and taja, a fungus, grows on leaves and branchlets (Gottlieb, 1976).
Conclusion
The leaves of the coca plant are used by Andean Indians to relieve fatigue and pangs of hunger, but also provide some nutritive value. Duke, Aulik & Plowman (1975) found that 100 gm of Bolivian coca leaves satisfied the dietary allowance for calcium, iron, phosphorous, vitamin A, vitamin B and vitamin E.
The Andean culture and the coca plant have thrived for centuries. It is ironic that this same plant that is used as a cure in its homeland is the source for so much abuse and misunderstanding in other parts of the world. (April Rottman)

La coca (Erythroxylon coca, Lam.) est une plante de famille des Érythroxylacées originaire du nord-ouest de l'Amérique du sud utilisée par les populations locales,souvent comme stimulant.
Hors d'Amériqueandine, elle est surtout utilisée pour un de ses alcaloïdes, la cocaïne, consommée comme stupéfiant et stimulant illégal. Mais elle contient en tout 14 alcaloïdes aux propriétés pharmaceutiques intéressantes.
Parmi ces principes actifs on peut énumérer :
▪ la papaïne, ferment qui aide à la digestion en l'accélérant,
▪ la higrine qui a des vertus sur la circulation sanguine, et protège du mal des montagnes,
▪ la quinoline qui évite la formation de caries dentaires lorsqu'elle est mélangée avec du calcium et du phosphore. (From Wikipedia)
Effets sur l'organisme
L'analyse phytochimique de la coca (Erythroxylum coca var. coca) cultivée en Bolivie laisse apparaître que celle-ci contient trois alcaloïdes naturels, parmi lesquels la cocaïne représente la quantité la plus importante. Cette teneur en cocaïne est égale quelle que soit la région de production et varie selon la saison de récolte des feuilles. La préférence des agriculteurs boliviens pour la coca des Yungas, la plus ancienne zone de culture en Bolivie, ne peut donc s'expliquer par une variation de la concentration en cocaïne mais pourrait être due, entre autres, aux qualités gustatives de la coca cultivée dans les Yungas et à l'ancienneté des réseaux commerciaux établis entre cette région et les marchés d'approvisionnement locaux.
La coca est réputée chez les montagnards des Andes donner des forces, aider à lutter contre le froid et les maladies. Les études physiologiques menées dans le cadre de ce programme ont permis de définir les effets majeurs de la mastication des feuilles de coca sur le métabolisme. Les analyses de prélèvements sanguins des consommateurs réguliers ont révélé que la mastication conduit à une ingestion d'une quantité de cocaïne non négligeable et susceptible d'être active dans l'organisme. Cette quantité est cependant bien inférieure à celle absorbée dans le cas d'une consommation illicite de cocaïne (crack, injection notamment).
L'étude clinique menée auprès d'une quarantaine de paysans de l'Altiplano, les uns consommateurs de coca et les autres non, a montré que si la mastication des feuilles ne contribue pas à augmenter les capacités physiques des mâcheurs, en revanche elle leur permet de soutenir un effort plus prolongé et stimule leur système respiratoire. Cet effet sur l'endurance a été observé uniquement chez des usagers réguliers de coca et non chez des consommateurs occasionnels. Cette plus grande résistance face à l'effort physique est attribuée à une meilleure circulation sanguine, à une action sur les catécholamines (médiateurs chimiques du système nerveux) et à une augmentation du nombre des globules rouges, qui favorisent une plus grande oxygénation des muscles. Par ailleurs, il a été observé que la consommation traditionnelle de feuilles de coca, considérée par certains comme un substitut alimentaire, ne provoque pas une diminution de l'appétit. Le régime alimentaire des consommateurs et non-consommateurs est ainsi similaire.
L'ensemble de ces résultats laisse apparaître que les bénéfices physiologiques tirés de la mastication de feuilles de coca contribuent à aider les populations andines à s'adapter à la vie en altitude et à endurer des conditions de travail rendues souvent très difficiles à ces hauteurs (Michel Sauvain, IRD).