Legalized medical cannabis in Washington Washington is one of the more than 20 US states that have legalized medical cannabis. It was approved about 16 years ago, in 1998. Since then, a lot of people residing in the state have taken advantage of the benefits of medical cannabis. The approval of the medical cannabis law in Washington lifted the criminal punishments against the possession, use, and growing of medical cannabis by people who have been screened and deemed qualified. License ...