In Colorado, cannabis has been legal for medical use since 2000 and for recreational use since late 2012. On November 7, 2000, 54% of Colorado voters approved Amendment 20, which amended the State Constitution to allow the use of marijuana in the state for approved patients with written medical consent. Under this law, patients may possess up to 2 ounces (57 g) of medical marijuana and may cultivate no more than six marijuana plants. Patients who were caught with more than this in their possession could argue "affirmative defense of medical necessity" but were not protected under state law with the rights of those who stayed within the guidelines set forth by the state. The Colorado Amendment 64, which was passed by voters on November 6, 2012, led to recreational legalization in December 2012 and state-licensed retail sales in January 2014. The policy has led to cannabis tourism. There are two sets of policies in Colorado relating to cannabis use: those for medicinal cannabis and for recreational drug use along with a third set of rules governing hemp.

Colorado Amendment 64 was a successful popular initiative ballot measure to amend the Constitution of the State of Colorado, outlining a statewide drug policy for cannabis. The measure passed on November 6, 2012, and along with a similar measure in Washington state, marked "an electoral first not only for America but for the world."