Authorities have arrested six people as part of a weeks­long investigation of synthetic cannabis sales that caused dozens of overdoses in downtown Minneapolis last month.

Three of the arrests were made in simultaneous raids shortly after 10 a.m. Thursday of a vehicle and a residence in the 2700 block of S. Chicago Avenue.

A 38-year-old St. Paul woman and a 47-year-old Minneapolis man were arrested on suspicion of felony drug possession after investigators found about a quarter-pound of synthetic pot, drug paraphernalia and some cash at the residence, according to the arrest report. The two suspects named in the report were booked into the county jail, where they remained Friday afternoon without bail. No court dates have been set.

In keeping with its policy, the Star Tribune isn't naming the suspects because they hadn't been charged as of Friday afternoon. An unidentified third suspect, a woman, was also arrested, but hadn't been charged as of Friday afternoon.

The other three suspects were each cited for misdemeanor offenses; their identities and circumstances of their arrests were not immediately available Friday.

Officer Corey Schmidt said that more arrests could follow Thursday's raids by officers from the First Precinct's community response team (CRT).

The investigation began after a spike in overdoses in two small areas of downtown Minneapolis: the intersections of 14th Street and Chicago Avenue and 5th Street and Hennepin Avenue. The synthetic cannabis mimics the effects of naturally grown marijuana but can be many times more potent.

Schmidt said it was too early to tell whether the suspects were part of the same drug-selling crew.

Hennepin County Medical Center's Dr. Jon Cole said 128 of the year's 177 documented synthetic cannabis overdoses happened in a roughly three-week span from the last week of September to mid-October. The majority of the cases occurred in Hennepin County, mostly in Minneapolis, and the patients were usually taken to HCMC for treatment. There have been no reports of fatalities.

"That means the vast majority of the year's cases, including the outbreak that happened in St. Paul at the end of May, happened all in Hennepin County and happened all in this cluster," said Cole, also the medical director of the Minnesota Poison Control System, the statewide agency that monitors drug overdoses. "So, it's pretty substantial."

Synthetic cannabis, commonly referred to as "K2" or "spice," is usually sold online and at convenience stores, head shops and gas stations. While many versions of the cheap, potent drug are already banned, authorities say regulation is difficult because manufacturers are constantly tweaking the recipes of their drugs to skirt existing laws.

For the same reasons, tracking outbreaks can be complicated, officials said.

The drug's effects can be dangerous, and in some cases life-threatening. A quickened heart rate and seizures are common side effects, but some users also experience extreme anxiety, paranoia and hallucination.

Paramedics responded to 125 emergency calls in Minneapolis for suspected K-2 overdoses over an eight-day period starting Sept. 30, according to Mike Trullinger, deputy chief of operations at Hennepin Emergency Medical Services. Calls for K2 overdoses have since waned, he said.

Last month, police zeroed in on a man, 44, as a suspect after an informant said he was dealing "dirty" K2 from a Brooklyn Center hotel room, according to court filings. Police later raided the hotel room, but it was unclear what, if anything, was seized.

It was unclear whether that man was among those arrested, but as of late Friday he hadn't been charged in connection with the overdoses.