A wave of heroin overdoses in just a 12-hour period Saturday in or near Anoka County left two people dead and four others taken to hospitals, one of them in critical condition.

Citing an "alarming number of overdose cases to happen so close together" in time and place, the Anoka County Sheriff's Office said in a statement that investigators are speculating that the overdoses could potentially be tied to the same single source of the drug.

Five of the six people who overdosed Saturday — four men and one woman — are in their mid-20s, authorities said. The sixth was a 30-year-old man. Two are from Fridley, while the others are from Anoka, Andover and Ham Lake. One is from Isanti but was taken to a hospital in Coon Rapids, according to the Sheriff's Office. Their identities were not released.

Meanwhile, across the metro, officials in Bloomington are assessing whether a few overdoses that occurred at the Mall of America on Friday night could be related.

Authorities responded to three people at the mall who became unconscious after using a combination of drugs together, including heroin, said Police Deputy Chief Mike Hartley. The combination of drugs was likely the cause of the overdoses, but Hartley said investigators intend to specifically examine the role that heroin played in the emergencies.

"This is out of the norm, and when that occurs it's obviously troubling to us," Hartley said.

Heroin deaths spiked dramatically across the country in the last decade, part of a dangerous epidemic of prescription and illicit opioid use. The Northeast and parts of the Ohio Valley have been particularly hard hit, but officials in Minnesota have been seeing big jumps in opioid abuse too.

Medical examiners in Anoka, Dakota, Hennepin, Ramsey, Scott, Sherburne, Wright and St. Louis counties reported at least 79 heroin overdose deaths to the DEA last year, compared to 16 in 2010.

Opioids include prescription medications used to treat pain, such as morphine, codeine, methadone, OxyContin, Percocet, Vicodin and buprenorphine, as well as illegal drugs such as heroin.

State officials are paying particular attention to how doctors prescribe narcotic painkillers that can themselves be addictive and dangerous. Those painkillers can also lead users to heroin; the American Society of Addiction Medicine estimates that four out of five new heroin users first began misusing prescription opioids.

In 2014, 10,574 people in the United States died from heroin-related overdoses, more than triple the count in 2010, according to the U.S. Drug Enforcement Administration.

Synthetic fentanyl, which recently began showing up in Minnesota, is being added to boost the potency of heroin in some cases. Nearly 50 times stronger than heroin, it's also boosting the lethality of the drugs being sold illegally.

Heroin's manufacture and distribution "are always illegal and the purity and conditions of the substance are never known by its user," the Anoka Sheriff's Office warned.

The office declined to release further details on Saturday's overdoses, saying, "the investigation is extremely difficult in that heroin users don't cooperate with police."

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