While cannabis plants have been grown since at least the 3rd millennium BCE, evidence suggests that it was being smoked for psychoactive effects at least 2,500 years ago in the Pamir Mountains; the earliest evidence found at a cemetery in what is today western China close to the tripoint with Tajikistan and Afghanistan. Since the early 20th century, cannabis has been subject to legal restrictions. The possession, use, and cultivation of cannabis is illegal in most countries of the world. In 2013, Uruguay became the first country to legalize recreational use of cannabis. Other countries to do so are Canada, Georgia, and South Africa, along with 11 states and the District of Columbia in the United States (though the drug remains federally illegal). Medical use of cannabis, requiring the approval of a physician, has been legalized in many countries.