Medical marijuana use and sales won't be prosecuted by the federal government, according to a new Justice Department memo from Deputy U.S. Attorney General David Ogden (inset, right).

But there's a catch: the federal directive only applies in states that have laws authorizing medical marijuana usage.

The DOJ also made clear that this new policy cannot be used as a 'get out of jail free card' by drug traffickers or those who grow pot on federal land.