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Marijuana consumption in Washington in 2013 is larger than the 85 metric tons (MT) previously projected by the Washington Office of Financial Management.

• Even before adjusting for survey undercounting, our estimates suggest a 90-percent confidence interval of approximately 120–175 MT. The difference is largely driven by our use of more recent data.

It is difficult to know by how much surveys understate actual consumption.

• Many of the relevant studies were published over a decade ago and times have changed; the NSDUH methodology has been improved substantially, and a national increase in marijuana use over the 2000s may have influenced willingness to self-report.
• It is also unclear how applicable national and regional studies are to the state of Washington. After reviewing the evidence and attempting to adjust for undercounting, results from our simulation suggest consumption likely falls within the interval of 135–225 MT, with a median estimate close to 175 MT.

Three counties account for about 50 percent of marijuana users in Washington.

• King County accounts for about 30 percent of the marijuana users, while Snohomish and Pierce counties each account for roughly 11 percent.

The literature is surprisingly thin concerning how much marijuana users consume during a typical day of use.

• That general deficit becomes all the more acute when focusing on a particular jurisdiction and time, such as Washington in 2013. The emphasis has traditionally been on counting users, not counting grams.
• However, by augmenting that thin literature with data from the web-based consumption survey developed by RAND, we estimate that Washington residents who use marijuana 21 or more times per month consume, on average, 1.3–1.9 grams during a typical use day.

Multiple datasets provide information about the potency of the marijuana consumed in Washington.

• None is ideal, and there is no way to take a random sample of the universe of marijuana that is sold or consumed. But the available information suggests that lower-potency forms account for only a modest share of the Washington market and probably a smaller share than they do nationwide.