At least 22 people between the ages of 16 and 19 were treated at hospitals near Boston following a concert by electronic dance musician Avicii got out of control.

Officials say a mix of drugs, alcohol, and heat lead to the teens becoming sick at TD Garden Center where Avicii was performing Wednesday night.

Signs of the popular club drug “Molly” – a form of ecstasy – were evident, according to witnesses, with concertgoers strapped to stretchers, some still screaming and flailing around, according to WCVB.

Chad Dyson, who attended the show with friends, told ABC News, “There was a girl all alone, she was passed out for some time. She was limp. Shortly after that, she started vomiting. They had EMS come by and actually took her away in a chair, strapped her down and took her out of the venue.”

Boston Police described the situation as a mass casualty event because of the number of people involved.  Dozens more were treated outside the venue as well.

The incident at TD Garden Center is not isolated. Drugs and alcohol sent nearly 30 people to the hospital at the Avicii concert in Toronto last month.

After the show, Avicii – whose real name is Tim Bergling – to to Twitter to extend his condolences to fans.

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