No deaths have been reported, but authorities say two people had life-threatening symptoms.
The man arrested on Wednesday is suspected of being connected to some of the drugs that caused the overdoses, NBC News Connecticut reported.
"After 8:00 [a.m. Wednesday] we ended up with 12 victims in a 40-minute period. That caused us to respond with a multi-casualty incident", New Haven Fire Chief John Alston said.
The New Haven Police Department is investigating the case.
Most of the people who overdosed Wednesday in New Haven were lower-income or homeless, Hartman told WTNH.
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Some victims were found unconscious, while others were nauseous or lethargic.
A similar, but smaller overdose incident, played out on the Green on July 4, when more than a dozen people became sick from synthetic marijuana, according to the Associated Press.
Three people were treated since midnight, according to New Haven Emergency Operations Director Rick Fontana, while a WVIT-TV crew saw emergency teams treating two people on New Haven Green on Thursday morning, including one person taken away on a stretcher. Three people who overdosed died after taking cocaine that had been laced with fentanyl, over a dozen others were hospitalized. "Don't put your life in harm".
The AP reports, "Paramedics and police officers remained at the park all day as more people fell ill. Emergency responders rushed to one victim as officials were giving a news conference nearby late Wednesday morning". "Let's address it that way", Alston said. 'Narcan was not effective here at the scene, ' said Alston.
"This was a particularly odd, rare occasion where (there was) call after call for man down, obviously with symptoms of some kind of overdose, and at the time of getting that patient packaged and transported to the hospital, we'd see another immediately fall down, right there", Lt. Ernest Jones said.
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The overdoses were initially feared to stem from a batch of synthetic marijuana, also known as K2 or Spice, possibly laced with an opioid.
Fontana also says that the DEA sample that was sent off for analysis came back negative for Fentanyl.
'We're eager to raise awareness at the highest levels of the federal government for a better sense of what happened and the challenges that urban centers face in terms of combatting a persistent, vexing presence of people with substance abuse disorder'.
Residents watched in horror as more than 70 people collapsed near a city park in Connecticut Tuesday night into Wednesday, overdosing on what authorities believe was a tainted batch of synthetic marijuana.
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