Research in Bolivia is helping to throw new light on coca, which has been used for centuries by Andean peoples as a remedy for tiredness, altitude sickness and staving off hunger.
It is also the raw material for cocaine. While much has been written about the illicit uses of coca, little is known about why Andean workers and peasants remain so attached to their traditional use of the plant. In Bolivia alone, nearly half of the seven million population are said habitually to take coca, either chewed or as tea.
A Franco-Bolivian research team based in La Paz is aiming to discover what are the actual effects of the coca leaf on its traditional consumers, the farmers.
The Project Coca is based at the Bolivian Institute of Biology at High Altitude, a leading research centre attached to La Paz's Universidad Mayor de San Andres. Headed by Bolivian and French scientists Mercedes Villena and Michel Sauvain, the project is funded by Orstrom, the French scientific co-operation agency.
Experiments have involved dividing 40 farmers from two highland communities into two groups, comprising regular coca-chewers and a control group of non-coca users. They were then asked to carry out various forms of exercise, such as riding bicycles, while the researchers measured their physiological reactions.
The team discovered that contrary to popular belief coca does not give greater strength, but increases physical resistance, enabling the coca-chewer to carry on working for longer. Similarly, coca does not act to suppress hunger, as although coca chewers reported loss of appetite and claimed they needed to eat less, they actually ate the same amount as the control group.
A third line of investigation centred on the plant's effectiveness as a remedy for altitude sickness, caused by the lower oxygen content of air at high altitudes.
People who are not acclimatised, or who over-exert themselves, find they have to breathe much faster to maintain an adequate supply of oxygen. This can cause imbalances in the blood supply leading to exhaustion, headaches and nausea.
New arrivals at La Paz airport, which at almost 4,000 metres above sea level is one of the highest in the world, are often badly affected and in such cases the traditional remedy is a cup of coca tea.
Tests carried out by the team revealed that coca does indeed have a positive effect as it acts to stimulate the respiratory centres, increases lung capacity and so enables the subject to cope better with the changes in the composition of the air.
A further project aim was to find out why coca-users prefer coca from one area of Bolivia. the Yungas, to that of another, the Chapare. As part of the fight against the cocaine trade Bolivia in 1988 limited the legal production of coca to specific areas, mainly the tropical valleys of the Yungas.
At least 90 per cent of production in Chapare is for illicit purposes. and various initiatives were unsuccessfully introduced to persuade farmers to switch crops.
It was thought research might establish an intrinsic difference between Yungas and Chapare coca, possibly a lower cocaine alkaloid content. If so, enforcing the law would be simpler as Yungas coca for legal consumption could be distinguished from its illicit cousin.
But the content was identical. Mr Sauvain believes that people's preference for Yungas coca is therefore attributable to other factors such as a sweeter taste. The team is now busy trying to determine whether long-term use of coca has a negative effect on the human organism and whether it creates physical addiction.