At least, authorities reported Wednesday. The majority of these overdoses happened on the New Haven Green -- a downtown park near Yale University -- throughout the day, according to officials.
Testing from the federal Drug Enforcement Administration found that the drug in question is K2, a potent, synthetic drug that induces a marijuana-like effect. The DEA also says there were no additives in the K2.
Officials in New Haven say no deaths have been reported, though at least six victims were near death.
What is synthetic marijuana?
Manufacturers started selling, often advertised as a safe "alternative" to marijuana, in the early 2000's. It is a class of designer drugs made up of psychoactive chemicals that are sprayed onto plant material. Synthetic marijuana is smoked, added to tea or food and eaten, or mixed into a liquid and vaped to produce a high. They mimic the effects of THC, the primary psychoactive compound naturally found in marijuana.
However, consumers don't know which chemical compounds are in the drugs, so toxicity and adverse effects can be unpredictable and vary widely. The products are often labeled as incense, herbal mixtures, or potpourri and sold openly under a variety of names like "K2," "Spice," "Mr. Nice Guy," and "Green Giant."
Why is synthetic marijuana so dangerous?
The chemical compounds in synthetic marijuana have been linked to a number of severe side effects, including seizures, psychosis and death. In 2017, a review of studies on synthetic marijuana published in the journal Trends in Pharmacological Sciences concluded that these compounds are more dangerous than pot.
Synthetic marijuana compounds "produce a variety of dangerous acute and chronic adverse effects… with a greater severity and frequency than observed following marijuana use," the researchers wrote in the review. As such, "K2/Spice products are clearly not safe marijuana alternatives," the researchers said.
Other commonly reported side effects include agitation, rapid heartbeat, lethargy, nausea, vomiting, confusion and headaches.
Other incidents involving synthetic marijuana
In recent years, synthetic weed has also been linked to a number of high-profile overdoses, as well as additional disturbing side effects. Earlier this year, the drug was linked to– from the nose, gums, and in urine – in the Chicago area.
In 2017, dozens of people with blank stares were observed stumbling around a Brooklyn neighborhood in an apparent.
New York City Mayor Bill de Blasio signed a law in 2015.
"This is a very risky substance that carries significant health consequences," Dr. Hillary Kunins, Assistant Commissioner at the New York City Department of Health and leader of the Bureau of Alcohol and Drug Use Prevention, Care and Treatment, told CBS News at the time. "We really want to educate the public that this is not a drug to be used lightly and that the effects are unpredictable and serious."
Synthetic marijuana a national issue
According to the Centers for Disease Control and Prevention, poison control centers across the country receive thousands of reports each year of adverse health effects from people who have used synthetic weed. The CDC says 2015 was the year with the highest number of calls at 7,794.
The federal government has banned many specific synthetic cannabinoids, while many state and local governments, including New York City, have passed their own laws targeting other synthetic cannabinoids, according to the CDC.
Health officials urge people not to use synthetic marijuana and to seek medical attention immediately if you or someone you know has become ill after using the drug.