Legalize it. Now.
The cruel irony of the America criminal system as it pertains to drug offenses is this: cocaine, a far more dangerous and far more addictive drug, is classified Schedule II, which means with the proper prescription, your doctor (or dentist!) can prescribe cocaine for use during medical procedures like operations.
Marijuana, by Federal law, is Schedule I. It cannot...I stress, cannot ever, be used legally in the United States.
Now, you ask how medical marijuana laws manage to get around that simple fact.
They don't. It's up to the Feds to enforce Federal law (which always trumps state law on these things). That they don't does not make medical marijuana legal. They ignore it. It doesn't exist.