More young people experiencing a psychiatric emergency began showing up in the emergency department of a Boston hospital with cannabis in their system after recreational marijuana was legalized than before, according to a new study.To Dr. Cheryl Foo, a psychologist at Mass General Brigham and one of the study authors, the results were “really startling.”The researchers examined health records from 7,350 people treated by Mass General Hospital’s psychiatric emergency service. They focused on those who tested positive for THC, comparing visits before recreational dispensaries opened — from Jan. 1, 2017, to Nov. 19, 2018 — to visits during the first year recreational marijuana was sold, from Nov. 20, 2018, to December 31, 2019.The impact on young people was clear: a 300 percent increase.”From 5 percent to nearly 20 percent of teenagers who had cannabis detected in their urine when they were coming in for a psychiatric emergency,” Foo said.Dr. Foo said researchers did not find such a dramatic jump in other age groups. “Cannabis commercialization, the increasing availability of cannabis and high potency cannabis is disproportionately affecting a vulnerable subgroup of teenagers of youths, particularly those who have mental health challenges,” Foo said.The research has been published in the American Journal of Preventive Medicine.In a series of stories this past June, 5 Investigates reported on what psychiatrists, counselors, and others who work with young people and mental health are seeing: that some young people’s frequent use of high-potency THC products is making them addicted to cannabis and leading to serious mental illness.”Psychotic like experiences, depression symptoms, anxiety symptoms, even suicidality as well,” said Foo, who also sees patients at Mass General Brigham as director of family services at MGB’s First Episode and Early Psychosis Program.”I would do it during school, then I would do it during work, then I would just do it pretty much all day,” was how one young person described how he would consume high-potency THC from vape cartridges as a teenager.He developed cannabis-induced psychosis.”I just felt really, really weird. I didn’t even know what was going on,” he said.”I thought I lost my son,” his mother said. “He wasn’t present. It was just this person that was completely manic and talking like someone that you would expect to see on the street, like a homeless person that’s talking to themselves and acting really crazy.”Foo and other clinicians tell 5 Investigates that parents coming to them for help frequently don’t understand the risks that high-potency cannabis has for damaging developing brains because it simply wasn’t around when parents were younger.But the Massachusetts Cannabis Control Commission, which regulates the industry, questioned the study. A Commission spokesperson said the agency is only responsible for regulated dispensaries, not black-market products or unregulated hemp products containing other forms of THC, and that the MGB study did not discern where emergency department patients got their cannabis.The Commission spokesperson also criticized the study for apparently incorrectly reporting on the number of dispensaries open during the period of time, and argued that the study was claiming legalization caused the increase in psychiatric issues. Educating the public is part of the Commission’s mandate, the spokesperson added, but the state hasn’t funded the Commission’s public awareness campaigns since the 2020 fiscal year.But Foo said she believes the study doesn’t capture the current impact of cannabis in Massachusetts, where the number of recreational dispensaries grew from nearly 40 the first year to nearly 400 now.””I really suspect that the impacts are much greater,” Foo said.