It is impossible to eradicate the traditional consumption of coca leaf in Andean countries. Over 2 million Bolivians "chew". This brings some questions forth: what physiological benefit do the consumers get from this habit in terms of adaptation to altitude (the Bolivian peasants live 4000m high), to effort and as food substitute? Scientists from the Bolivian Altitude Biology Institute, the CNRS and the ORSTOM, supported by the French Ministry for Foreign Affairs, have tried to answer these questions with experimentations that involved coca consumers. The results obtained are twofold: the cocaine content cocaine of coca leaves is the same everywhere, whether it is grown for traditional consumption or for drug traffic. In terms of benefits on human health, chewing helps physiologically to breathe better in altitude, it allows longer efforts for chewers than non-chewers, and does not affect food consumption.