Don't assume that Cole Memorandum covers all relevant interactions, though. Aside from the more obvious federal laws that directly criminalize use of drugs, there are others that make other activities illegal when drugs are involved. It's not just the DEA that's on the bandwagon.
For example, when purchasing a firearm, one of the questions on the form that has to be filled is this:
"Are you an unlawful user of, or addicted to, marijuana or any depressant, stimulant, narcotic drug, or any other controlled substance?
WARNING: The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside."
(That disclaimer was added long after the memorandum you mention, by the way.)
The ATF has since decided that a mere possession of a medical marijuana card constitutes prima facie evidence of being "unlawful user of".
For example, when purchasing a firearm, one of the questions on the form that has to be filled is this:
"Are you an unlawful user of, or addicted to, marijuana or any depressant, stimulant, narcotic drug, or any other controlled substance?
WARNING: The use or possession of marijuana remains unlawful under Federal law regardless of whether it has been legalized or decriminalized for medicinal or recreational purposes in the state where you reside."
(That disclaimer was added long after the memorandum you mention, by the way.)
The ATF has since decided that a mere possession of a medical marijuana card constitutes prima facie evidence of being "unlawful user of".