The first marijuana law was passed in 1937. Interestingly, the Gov't still respected the Cosntitution enough to ban it in the form of a tax law (thus, it was known as the Marijuana Tax Stamp Act). Harry J. Ainslinger and the Federal Bureau of Narcotics boys were really in a quandary over how to get this accomplished without raising the dreaded "P" word (Prohibition, which, when repealed, coincidentally put ol' Harry out of a job), but were ecstatic to find precedence for passing a law requiring a Tax Stamp for an item, and then refusing to issue the Stamps, thereby de facto outlawing said item. The model which they were so happy to discover was the Machine Gun Tax Stamp from a few years earlier.Both of these laws were, as mentioned, passed to give the Prohibition bureaucracy something to do. "Unintended Consequences" has an excellent review of the (non)constitutionality of the 1934 Gun Control Act.
-Eric
The answer is not that the 14th Amendment grafted the federal bill of rights onto the states, because that would simply mean that the states were protected from "Congress" making any law respecting religion - a right they already had. It may have something to do with the privileges and immunities clause, but I don't know.
A clear answer or cite to a case would be greatly appreciated.