Overdoses on synthetic cannabis sent people to the hospital in Minneapolis at least 60 times last week, causing hallucinations and violent behavior in some users, while leaving others nearly "comatose," health officials said.

The number of emergency calls involving suspected overdoses in the city was double that number, from midnight Sept. 29 through Sunday afternoon, officials said.

"This is the biggest outbreak in Minnesota that I'm aware of since 2015," said Dr. Jon Cole, medical director of the Minnesota Poison Control System, the statewide agency that monitors drug overdoses. "This alone is going to change the numbers from 2017 and would increase it almost certainly from 2016."

So far, none of the cases has been fatal, officials said.

The vast majority of the patients were treated at Hennepin County Medical Center, said Cole, a physician there. A spokesman for North Memorial Medical Center in Robbinsdale declined to say Monday whether the hospital had also seen a recent increase in emergency room admissions for synthetic cannabis — commonly referred to as "K-2" or "Spice" — saying that such statistics weren't readily available.

While many versions are illegal, the cheap, potent drug is sold online and at convenience stores, head shops and gas stations with exotic-sounding nicknames like "AK-47" and "Scooby Snax." Its effects, authorities say, can be dangerous, and in some cases life-threatening. A quickened heart rate and seizures are common side effects.

Still, while the number of hospital admissions for synthetic cannabis is far below those for highly addictive "hard" drugs like heroin and cocaine, the startling spike in the number of people overdosing on K-2 has local officials' attention.

"It would be much more typical for us to have one [or] maybe two in one day," said Cole.

All of the reported cases occurred in the west metro, he said. Last summer, K-2 was blamed for a number of overdoses near the old Dorothy Day homeless shelter in downtown St. Paul.

Police scanner traffic suggested that at least four people overdosed on K-2 at a downtown Minneapolis light-rail station one afternoon last week.

Regulation is difficult, authorities say, because the drugs' manufacturers are constantly tweaking the recipes of their drugs, which mimic the effects of naturally grown marijuana but can be many times more potent, to skirt existing laws.

And unlike with opioids, the effects of which can be reversed with the drug naloxone, there is no antidote for the various versions of synthetic cannabis available on the streets, he said. Each patient is treated on a case-by-case basis, based on his or her symptoms, he said. Cole said that some users hallucinate and become anxious and violent, while others turn "comatose," their heart rates dropping well below normal.

Authorities have seen a surge in overdoses nationally from drugs. They're also having a harder time keeping up with manufacturers, who continue to create new chemical compounds to evade detection.

In 2015 alone, the DEA's National Forensic Laboratory Information System, which collects data on seized drugs tested by local, state, and federal forensic laboratories, identified 84 new synthetic versions of pot. That year, authorities saw a dramatic spike in the number of synthetic cannabinoids-related cases, including in Minnesota, but mostly in southern states like Mississippi and along the East Coast.

But, synthetic drug use had actually decreased across Minnesota recently, falling from 223 "exposures" in 2015 to 83 last year, according to this year's Drug Abuse Trends report by addiction expert Carol Falkowski.

Samples of the drugs from the latest rash of overdoses in Minneapolis were sent to the state Bureau of Criminal Apprehension to determine the composition.

Jill Oliveira, a spokeswoman for the BCA, said that the agency's forensic laboratory hadn't seen an increase "in synthetic cannabinoids evidence testing submissions."

"Our agents currently are not involved in an investigation regarding K2," she said in an e-mail.

E-mails to three Minneapolis police spokespeople on Monday were returned with an out of office message saying that the department's press office was closed for the holiday and that they would only respond to messages that were "critical in nature."

Over an eight-day period starting Sept. 30, paramedics responded to 125 emergency calls in Minneapolis for suspected K-2 overdoses, according to Mike Trullinger, deputy chief of operations at Hennepin Emergency Medical Services.

The agency had averaged two to three such calls per month since the beginning of the year, he said.

Most of the overdoses were concentrated in downtown Minneapolis, Trullinger said, with one nearby neighborhood responsible for 26 K-2-related calls. In several cases, disoriented users, hopped up on the synthetic drugs — which are coated with chemicals like acetone and smuggled from places like China — have attacked emergency responders, Trullinger said. Many times, paramedics responding to overdose calls are seeing the same faces, he said.

"Some of these are repeat patients who are literally released from the hospital, go back to the same area and buy more drugs and are again admitted to the hospital," he said Monday.

Libor Jany • 612-673-4064 Twitter:@StribJany