Two years ago, by way of voter referendum, Arizona voters passed a medical marijuana law similar to California and other states that allowed certain individuals with medical conditions to use grow and use marijuana. But just like those other states, while the state may have legalized marijuana grow and use, it is still a violation of federal law.
One would assume, however, that it is up to the federal government whether or not to enforce federal law. That is exactly what the United States Supreme Court decided when they said Arizona could not impose state penalties for violation of federal immigration law under SB 1070 (see "Supreme Court upholds Arizona SB 1070 in part, but does it matter?").
Having stated that though, it does not seem like 12 out 15 Arizona county attorneys agree with that legal principle (see "Medical-marijuana growers await outcome of Arizona lottery for dispensaries" by Yvonne Wingett Sanchez):
Yavapai County Attorney Sheila Polk, who has urged Brewer to halt licensing of dispensaries because marijuana is illegal under federal law... Polk and 12 of the state's 15 county attorneys are fighting the marijuana law and sought a legal opinion from Attorney General Tom Horne as to whether the state law is pre-empted by federal law.
Horne on Monday issued an opinion that the law's provisions "authorizing any cultivating, selling and dispensing of marijuana" are pre-empted but that issuing registry cards to patients and caregivers is not.
My own feeling is that people can disagree about whether medical marijuana is a good idea, but once the voters have spoken directly through a plebiscite, state officials have no business deciding on their own to enforce federal law. My hope is that the 15 county attorneys and Arizona Attorney General Thomas Horne will allow the voice of the people to stand unfettered.