With regards to Article I, Section 8 power to "regulate commerce among the several states" in the constitution... The ability for the Federal Government to regulate Marijuana, similar to Wickard vs Filburn and Wheat, is because Marijuana could be transported across state lines for re-sale thus allowing the Federal government to regulate the growing of Marijuana.
However, in Nevada for example, an individual has already purchased the Marijuana, paid state tax on that Marijuana and has a state recognized legal receipt of that Marijuana.
The question is, does the Federal Government have a case against that individual? The individual has already purchased the goods for personal consumption: no
