At least 22 teenagers attending an electronic dance music show in Boston were sent to the hospital on Wednesday. Many of them were suffering from a combination of alcohol and heat, ABC News reports.

Dozens more concertgoers were treated onsite. Signs of Molly and other illicit drugs were apparent, the article notes.

Organizers of summer music festivals are increasing drug screening, after four people died at festivals last year. The deaths were linked to Molly. Concertgoers should expect sniffer dogs, pat-downs and other drug screening measures. Music festivals will provide medical tents with doctors, nurses and emergency medical technicians.

In April, organizers of New York’s Electric Zoo three-day event said this year fans will be required to view an anti-drug public service announcement online in order for their festival wristbands to activate. The event will start later in the day, to reduce exposure to the sun. In addition, the organizers will scrutinize vendors more closely. The festival may place “amnesty bins” at the gates, so fans can drop off illicit substances before they are searched.

In 2013, the last day of Electric Zoo was canceled after two concertgoers died after taking Molly. Medical experts say club drugs are especially dangerous when they are taken in warm temperatures by people who are dehydrated and who exert themselves at all-day events.

Last year’s Electric Zoo festival included safety measures such as on-site emergency treatment centers, free bottled water, and periodic safety announcements. After the event, the promoters brought together an advisory board of doctors, security consultants and DJs to prevent future drug-related deaths.