It will likely take years for Massachusetts to put a dent in the illicit marijuana market, according to a researcher who found that to be the case in Washington state.

Three years after state-licensed cannabis stores in Washington opened in July 2014, roughly half of the recreational and medical marijuana consumed by residents was still coming from the illicit market, said Beau Kilmer, director of the RAND Drug Policy Research Center.

“You’re not going to eliminate the illicit market overnight,” Kilmer said. “It’s going to take years.”

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