"Not surprisingly, the Obama Administration would have been more successful had it simply legalized medical marijuana.143 In fact, the CSA [Controlled Substances Act] authorizes the Attorney General to do so, in consultation with the Secretary of Health and Human Services and the DEA.144 In other words, the President would not need the consent of the Congress to make this, more fundamental change to federal law."

Source

Miklos, Robert A., "A Critical Appraisal of the Department of Justice's New Approach to Medical Marijuana" (February 23, 2011). Stanford Law & Policy Review, Vol. 201, p. 101, 2011 ; Vanderbilt Public Law Research Paper No. 11-07, pp. 665-666.
http://papers.ssrn.com/sol3/D…