Since Amendment 64 passed in November 2012, Colorado residents age 21 and older can possess up to 1 ounce of retail marijuana. Colorado's first licensed retail marijuana stores opened January 1, 2014. Non-residents can purchase up to 1/4 of an ounce of marijuana at a time.
As of 2015, it remains illegal in Colorado to consume marijuana in public or in or around a licensed store, as well as indoor-but-public locations such as bars, restaurants and common areas in buildings.
In 2014, Nebraska and Oklahoma filed a federal lawsuit asking the U.S. Supreme Court to strike down Colorado's licensing of retail marijuana stores, claiming that the legalization of marijuana in Colorado caused an increase of marijuana possession in each state, which their police forces are ill-equipped to handle.