Earlier this week, Maryland Gov. Martin O'Malley signed into law a bill that revamps the state's previously-stalled medical marijuana program. Even though officials say patients may not be able to legally buy the drug for more than a year, the legislation makes Maryland the nation's 21st state to officially embrace medical marijuana.

Meanwhile in Colorado, where medical marijuana has been legal since 2000, state regulators are moving to shut down four medical marijuana business that were raided by the federal government.

Correction: A previous version of this map did not include New Jersey and Michigan, which have legalized medical marijuana.