And if a 'medical marijuana' user is not in precise compliance with its State laws for medical marijuana, the Feds can still prosecute.

"Given this context and the restriction of the relevant laws to those that authorize conduct, we conclude that § 542 prohibits the federal government only from preventing the implementation of those specific rules of state law that authorize the use, distribution, possession, or cultivation of medical marijuana. 

 DOJ does not prevent the implementation of rules authorizing conduct when it prosecutes individuals who engage in conduct unauthorized under state medical marijuana laws.  

Individuals who do not strictly comply with all state-law conditions regarding the use, distribution, possession, and cultivation of medical marijuana have engaged in conduct that is unauthorized, and prosecuting such individuals does not violate § 542."