In 2003, Seattle voters passed Initiative 75 to make marijuana offences the "City's lowest law enforcement priority." Ordinance 121509 was adopted by the Seattle City Council to establish a "sensible marijuana law enforcement policy." An eleven member Marijuana Policy Review Panel was established to assess and report on the effects of this ordinance and the implementation of I-75. The Panel was required to include two members of the City Council, two citizen members, one drug abuse prevention counselor, one harm reduction advocate, one representative of the Seattle Police Department, two criminal defense attorneys, one representative of the King County Prosecuting Attorney's Office and one representative of the Seattle City Attorney's Office.

In their final report, the Panel concluded that there were reductions in marijuana-related offenses, but were unable to conclude definitively that these reductions were attributable to I-75's passage. The Panel also collected and analyzed data to determine whether implementation of the ordinance would impact public safety, public health, public administration, or have any adverse fiscal ramifications. They concluded that there was no evidence of any adverse effect of the implementation of I-75 in any of the substantive areas examined. The MPRP was disbanded after their final report in 2007. In 2012, Washington and Colorado became the first U.S. states to legalize recreational use of marijuana. Washington had previously legalized medical marijuana in 1998. Under state law, cannabis is legal for medical purposes and for any purpose by adults over 21.