"A drug, broadly speaking, is any chemical substance that, when absorbed into the body of a living organism, alters normal bodily function.[5] There is no single, precise definition, as there are different meanings in medicine, government regulations, and colloquial usage.[6]" and from the same article "Coffee is the most widely used psychotropic beverage in the world. In 1999 the average consumption of coffee was 3.5 cups per day per U.S. citizen.[1]"
Also, "Many natural substances such as beers, wines, and some mushrooms, blur the line between food and drugs, as when ingested they affect the functioning of both mind and body."