Medical marijuana users risk job loss

 When a rare form of cancer invaded Joseph Casias' nasal cavity and his brain, his doctor prescribed marijuana to help alleviate the daily pain.

Casias lives in Michigan, where medical marijuana is legal.

But his employer, Wal-Mart, the nation's largest retailer, fired him in November 2009 after he failed a drug test.

Casias, 29, says he never came to work high. He's got a medical marijuana card to prove he's allowed to smoke legally in the state.