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Chicago public health officials are advising Lollapalooza-goers to test their drugs to make sure they’re not laced with fentanyl.

The Chicago Department of Public Health issued a warning a day before the four-day music festival began in Grant Park.

“ATTN CHICAGO & LOLLA FANS,” read a tweet from CDPH. “Fentanyl is a strong opioid that can easily cause an overdose. Test your medication before you use it, carry Narcan and don’t use it alone. If you suspect someone is overdosing, call 911.”

CDPH said fentanyl is found in cocaine, MDMA and other drugs – not just heroin. The department also said Narcan and fentanyl test strips can be picked up at Chicago public libraries in “readily accessible Narcan dispenser kits.”

America’s fentanyl crisis increasingly involves coroners, medical examiners and more

Narcan, also known as naloxone, is a drug used to reverse overdose symptoms and save lives. Opioid overdoses typically include low blood pressure, slow heart rate, slow or stopped breathing, blue lips, and pale skin.

Fentanyl, a synthetic opioid, has been the leading cause of overdose deaths across the US in recent years. A dose of just 2 mg is enough to kill a user with zero tolerance, while 60 mg of heroin is considered a lethal dose.

A general view of the crowd on the first day of the Lollapalooza music festival.

A general view of the crowd on the first day of the Lollapalooza music festival.
(Photo by Rob Grabowski/Invision/AP)

There were nearly 1,300 fatal fentanyl poisonings last year in Chicago alone. The DEA warned last week that fentanyl would almost certainly be present at the Lollapalooza festival.

“There will be people walking around at Lollapalooza with backpacks selling fentanyl pills. There’s no doubt in my mind,” Shane Caton of the Chicago DEA told Fox 32. It’s like Christmas for drug traffickers.”

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The annual music festival starts on Thursday and ends on Sunday, July 31.

Fox News’ Andrew Mark Miller contributed to this report.