The prohibition of the use of the coca leaf except for medical or scientific purposes was established by the United Nations in the 1961 Single Convention on Narcotic Drugs. The coca leaf is listed on Schedule I of the 1961 Single Convention together with cocaine and heroin. The Convention determined that "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" (Article 26), and that, "Coca leaf chewing must be abolished within twenty-five years from the coming into force of this Convention" (Article 49, 2.e).