Cannabis in Oregon is legal for both medical and recreational use. In recent decades, the U.S. state of Oregon has had a number of legislative, legal and cultural events surrounding the use of cannabis (marijuana, hashish, THC, kief, etc.). Oregon was the first state to decriminalize the possession of small amounts of cannabis and authorize its use for medical purposes. An attempt to recriminalize the possession of small amounts of cannabis was turned down by Oregon voters in 1997.

From 1999 through 2005, the ratio of Oregonians using cannabis outpaced the general United States population by 32–45%. In surveys conducted in 1974 and 1975—one and two years after decriminalization—it was found that 2% of respondents said they did not use marijuana or cannabis because it was unavailable, 4% for legal or law enforcement reasons, 53% reported lack of interest, and 23% cited health dangers. The remaining 19% were using or had used it at one time.

Measure 91 was approved in 2014 by 56% of the vote, legalizing non-medical cultivation and uses of marijuana. It followed perennial and unsuccessful efforts to legalize marijuana by ballot initiative, including in 1986 and in 2012 which made it to the ballot, but voters rejected.

In 2015, Oregon Governor Kate Brown signed an emergency bill declaring marijuana sales legal to recreational users from dispensaries starting October 1, 2015. State officials began working on establishing a regulatory structure for sales of marijuana, and taxing of such sales, restructuring the existing Oregon Liquor Control Commission into the Oregon Liquor and Cannabis Commission (OLCC) to oversee it. Effective January 1, 2017, dispensaries were no longer permitted to sell cannabis for recreational use unless they applied for, and received, an OLCC license for such sales. During the one-month span from early December 2016 to early January 2017, the number of retailers licensed to sell recreational marijuana grew from 99 to 260, and hundreds more applications were received and being processed.

According to the Drug Enforcement Administration (DEA), cannabis is readily available in Oregon. According to a 2006 report by the Substance Abuse and Mental Health Services Administration, in 2003–2004, Oregon ranked in the top fifth of states for cannabis usage in three age categories: 12 to 17, 18 to 25, and 26 and older. In 2005, while most states that had passed medical marijuana bills over the past decade saw marijuana use among teenagers decline faster than the national average (a 43% decrease), Oregon, Nevada, and Maine saw smaller decreases than the average.

The Substance Abuse and Mental Health Services Administration estimates and publishes the number of people to have used cannabis in the previous 30 days, as compiled by the Oregon chapter of the National Organization for the Reform of Marijuana Laws (NORML):

Large indoor and outdoor growing operations have been discovered on private, state, and forest lands, with plants numbering in thousands. Allegedly, large outdoor growing operations run by Mexican cartels drug trafficking were assumed to be operating in remote locations. Highly potent cannabis grown in Oregon is consumed locally, and distributed to other parts of the U.S.

In 1988, due to the success of the DEA's Campaign against Marijuana Planting in California, Oregon rivaled California nationally in cannabis production. In the 1990s, Oregon was a national leader in indoor cannabis cultivation, along with California, Washington, Kentucky and South Florida. For the decade ending in 1991, the DEA considered Oregon the "nation's cradle of indoor marijuana growing." In 2006, Oregon was the fourth largest indoor cannabis producing state, and the tenth largest cannabis producing state overall.