What’s the number one city for pot consumption in Canada? To figure that out, Canadian officials looked at number two.

Statistics Canada tested Canadians’ poop this year to see how much cannabis residents of five of the country’s largest cities — about 8.4 million citizens total — were using. The pilot programs, which ran from March to August, used a relatively new technique called wastewater epidemiology to examine sewage from 15 treatment plants.

Statistics Canada says that when anyone consumes marijuana, their body processes the main psychoactive ingredient tetrahydrocannabinol, or THC, into metabolites that are typically “flushed into the municipal wastewater system.” By analyzing the THC metabolites, the government is able to estimate the amount of pot people in the region are consuming. Europe has used a similar technique for more than a decade to determine drug consumption in major cities.

The answer to the burning question: On average, each person in the test consumed about 540 micrograms a week, or 0.2 grams a year, which isn’t very much. Overall, the government guesses that citizens of the five cities consume roughly 4,500 grams of pot a week in total — though with a margin of error of roughly 1,700 grams in either direction. The margin of error is high because sewage-based cannabis estimates were “highly sensitive to the excretion rate and THC potency,” Statistics Canada said.

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Defying West Coast stereotypes, Vancouver consumed the least amount of weed per capita, according to the Statistics Canada pilot, whereas Montreal and Halifax consumed the most. Toronto and Edmonton were the two other cities included in the study.

Statistics Canada cautioned that the tests are still experimental but said that the pilot was one of many ways the agency is figuring out how to study cannabis in Canada, which was made legal for recreational sale this fall after nearly a century of prohibition. By itself, this pilot measuring the amount of weed in the country’s poop is insufficient to figure out how much pot Canadians use, but it’s another tool the agency can use.

Statistics Canada has previously used other methodologies to estimate that the country consumed roughly 773 metric tons of cannabis in 2017, though acknowledged that figure was likely on the low end.

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