According to Issues & Controversies' article, marijuana "...has been illegal in the U.S. since Congress passed the Marijuana Tax Act in 1937."¹ You can learn more about marijuana's history in U.S. legislation and the controversies surrounding marijuana use through the Issues & Controversies and similar databases, as well as other library resources. I especiall recommend Opposing Viewpoints.
If you are asked to log in, to view an article or databases, your username would be your LOLA# and your password would be your birthdate formatted MMDDYY.