On November 6, 2012, I-502 was approved by a vote of 55.7% to 44.3%. Possession of up to 1 ounce (28 g) of marijuana by adults became legal under state law on December 6, however cultivation, sale and even gifting remained illegal. Laws regarding medical marijuana remained unchanged. After I-502 went into effect, the Washington State Liquor Control board began establishing regulations for the new recreational cannabis industry, with a deadline of December 1, 2013 set by the initiative.

In August 2013, the United States Department of Justice announced that it would not interfere with state-level legalization, as long as distribution and sales were strictly regulated by the state.[40] On November 18, 2013, the state began accepting applications for marijuana businesses including growers, processors and retail outlets. The Liquor Control Board initially planned to allow 334 retail stores and 2,000,000 square feet (190,000 m2) of growing space statewide.[41] The first recreational cannabis stores in Washington opened to the public on July 8, 2014.[42]