In defense of the coca leaf. Coca farmers and users band together in Bolivia in defense of what they call the sacred leaf, which has been banned by the Vienna Convention for links to cocaine. In La Paz they crowded the streets. The demonstration came on the day that the nation's President, Evo Morales, was speaking in defense of coca at a United Nations anti-drugs convention in Vienna. They displayed the many uses of the coca leaf, including soft drinks.