Cannabis use increased and substantially shifted from the illicit market since retail sales began in 2014, finds a new study based on analysis of public wastewater samples from Western Washington, suggesting that many established users switched very quickly from the illegal to the legal market.

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Cannabis use increased and substantially shifted from the illicit market since retail sales began in 2014, finds a new study based on analysis of public wastewater samples from Western Washington, suggesting that many established users switched very quickly from the illegal to the legal market.