Is cannabis legal in Washington DC? Yes, cannabis is legal in the nation's capital. The Legalization of Marijuana for Medical Treatment Amendment Act of 2010 was signed on May 21, 2010, after receiving a 13-0 vote from the Council of the District of Columbia.  Who can use medical cannabis in DC? Only qualified people are allowed to use or possess medical cannabis in DC. They have to register with the Health Regulation and Licensing Administration and receive their medical cannabis ...