THE ANDEAN PEOPLE AND THE COCA LEAF.

The Andean people, specially those living at a very high altitude, has made fundamental changes in their genes to deal with their harsh environment. To cope with the strenuous activities at such high altitudes the use of the coca leaf for medicinal purposes has been a centuries-old tradition.
The coca shrub grows wild across regions of Central and South Andean mountains. The antiquity of its use as a chewing leaf has been confirmed through carbon dating of mummified human remains more than 3,000 years ago, and being an important part of the daily life of the Andean people.
The chewing of the coca leaf provides risk-free benefits to the body of the Andean people when they are participating in remote wilderness activities and are exposed to the physical and environmental challenges inherent to the geographical scenario. The most widely publicized effect of the chewing leaf is its function in increasing work capacity, including reduction of bodily fatigue and the alleviation of thirst and hunger.
There are more than 1.1 million visitors to Machu Picchu (altitude 2,430m) and Cuzco (altitude 3,400m), Peru every year along with sold-out permits for the high altitude Inca Trail. Travelers often ascend to the city from sea level on commercial flights lasting less than 1 hour. Coca leaf tea is frequently recommended by local tourist industry and by travelers word of mouth for the symptomatic relief of acute mountain sickness.
High Altitude environments can be debilitating to un-acclimatized individuals exposed to elevations above 3,000m for periods ranging from several hours to days. The decreasing barometric pressure lowers the density of the air. The higher you go, the more the air thins.
Moderate hypoxia induces substantial alterations in physiological and psychological parameters within few hours to those who attempt to climb the Andean mountains. A lot of cognitive issues that the individual faces after climbing are almost like a hangover and it could take a couple of weeks or a month or so before they start to feel more articulated and capable of carrying on a coherent conversation.  Immediately upon ascent to high altitude, there is decrease blood oxygenation, which reduces the oxygen supply throughout the periphery and the brain. Adverse changes in mood states, as well as impairment in mental performance, occur during such altitude exposure, depending not only on the altitude and rate of climb, but also on the length of stay and effort expended to reach the desire altitude. Only sleepiness changed at 1,600m with the individual becoming sleepier compared to sea level. However, by day 2 after ascent to 4,300m, the initial mood experienced is euphoria, followed by depression. Subjects become less friendly, less clear thinking, and dizzier and with time, they may also become aggressive, unhappy, quarrelsome, anxious, and apathetic. Although, the body compensates, at least in part, for the lack of oxygen with a variety of physiological responses and adjustments.
The use of the coca leaf has long been viewed in the Andean culture as a remedy for symptoms experienced when traveling or working at high altitude. When a powerful community of people  has venerated a particular practice for thousands of years, it stands to reason that there is more to discover about its functional advantage over brain waives performance at such very high altitudes.