A doctor at one hospital says some patients tested positive for fentanyl, but it appears most of the overdoses were caused by a potent batch of straight K2 synthetic marijuana, also known as Kush. Three of the people who overdosed died after taking cocaine that had been laced with fentanyl, over a dozen others were hospitalized.
"We literally had people running around the Green providing treatment", said Rick Fontana, the city's emergency operations director, according to The Associated Press. "It's a nationwide problem that people are self-medicating for several different reasons, and every agency - police, fire, medical hospitals - all are strained at this time".
Fontana said the city's 911 center started receiving calls just after 8 a.m. about possible overdoses at the park.
Police said they arrested a person of interest in connection with the mass overdose. "Some of the reactions of the patients in the emergency department would suggest that there was an opioid involved as well", Bogucki told reporters during a news conference Wednesday.
In a warning last month signed by top federal officials, the Food and Drug Administration said synthetic marijuana has become particularly risky because some producers have been adding brodifacoum - a long-acting anticoagulant thought to extend the drug-induced "high". They say no deaths have been reported so far, but at least six victims were near death.
The victims ranged in age; however, many are part of the homeless population in the city, police said. Hawk said some people got better with the help of naloxone, an opioid overdose reversal drug, while others didn't. Three of those who overdosed are still in critical condition.
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New Haven police said one person is in custody.
Connecticut Gov. Dannel Malloy tweeted that the emergency in New Haven was "deeply troubling and illustrative of the very real and serious threat that illicit street drugs pose to health of individuals".
Fentanyl is approved as an anaesthetic and for pain relief, but its high profit margin for traffickers has made it a key drug in the USA opioid crisis.
These can include extreme anxiety, confusion, paranoia and even hallucinations.
"We want people to be warned that what they have could be extremely unsafe and they should not use it", he said. "I've never seen anything quite this bad happening at once". "This is a problem that's not going away", New Haven Fire Chief John Alston Jr. said, according to WVIT.
"One of our fears is that this isn't over", Hartman said.