You honestly think that's a trivial task?
Yes.
People caught driving under the influence of marijuana can and already are prosecuted under the same DUI laws as alcohol.
Companies will become the manufacturers and distributors of marijuana. Think people will scorn them? Nah. Philip Morris, one of the largest US cigarette manufacturers, also owns Kraft Foods, Kool-Aid, Nabisco, Oscar Meyer, and Maxwell House (among others). These same companies already have a large distribution infrastructure.
The government will get free money and will save millions a year on infrastructure costs by letting the potheads (the ones in jail just for using/posession) will be let out.