Feel free to enumerate any that would require the federal government to enforce marijuana laws. If there were any, I would have expected them to be mentioned in Gonzales v Raich, but none were.
I know of the "Single Convention on Narcotic Drugs" and the "United Nations Convention Against Illicit Traffic in Narcotic Drugs and Psychotropic Substances", but I am no lawyer so I can't say whether these treaties have a legally binding effect which prevents more relaxed dealing with drugs.