Show me in the Constitution where FedGov has the authority to dictate drug law or policy that doesn’t cross State Lines. (Spoiler: it’s not there.)
Wickard v. Filburn (1942) pretty much blew away any limitation on the federal government’s use of the commerce clause. In that case even a farmer’s subsistence crop of wheat for personal use was found to be in violation of a federal wheat quota because such activity in aggregate could hypothetically affect national prices. If that can be regulated as interstate commerce surely all cannabis production and consumption can as well.