More than 20 prescription medicines containing marijuana were sold in U.S. pharmacies at the turn of the 20th century. Pot based medications were commonly available until 1942, when cannabis was stricken from the U.S. Pharmacopeia, the official compendium of drugs considered effective. From 1937 to 1942 the federal government collected a tax of $1 per ounce for such drugs. - US News
