What about the 10th amendment?
Medical marijuana laws
As of November 2010, 15 states (Alaska, Arizona, California, Colorado, Hawaii, Maine, Michigan, Montana, Nevada, New Jersey, New Mexico, Oregon, Rhode Island, Vermont, and Washington) and the District of Columbia have passed legislation which permit the use of medical marijuana.[15] California Proposition 19 would have gone one step further, and legalized marijuana use by persons over age 21 for any purpose whatsoever;[16] however, the state constitutional amendment did not pass.
The Obama administration announced in October 2009 that it advised federal prosecutors not to target medicinal marijuana users, or their suppliers, in states that have passed such laws.[17][18]
Despite this campaign promise, the DEA has continued to raid medical facilities in several states,[19][20][21] and the DOJ has gone so far as to prevent such cases from being well publicized.[22]