Connecticut officials are urging cannabis smokers to exercise caution, after health experts reported the first documented case of fentanyl-tainted marijuana.

The State Department of Public Health issued the warning earlier this week, about five months after Connecticut legalized recreational marijuana use. According to CBS News, officials have confirmed nearly 40 opioid overdoses in the state from July through October. Each of these patients reportedly exhibited signs of an opioid overdose and required naloxone for revival; however, they all denied consuming any drug other than marijuana during the four months prior to their overdoses.

In one of the cases, authorities were able to collect a sample of the weed in question. They later determined the sample contained fentanyl—a powerful synthetic opioid that is up to 100 times more concentrated than morphine. According to NBC Connecticut, the drug is also the leading cause of overdose deaths in the state.

“This is the first lab-confirmed case of marijuana with fentanyl in Connecticut and possibly the first confirmed case in the United States,” DPH Commissioner Manisha Juthani, MD, said in a press release.

The department did not mention whether they collected samples from the other 38 cases.

News of the investigation comes after the Centers for Disease Control and Prevention reported a record number of drug overdose deaths in the country. According the agency, an estimated 100,300 Americans died from an overdose between May 2020 and April 2021, marking a nearly 30 percent increase from the previous year.

President Joe Biden addressed the unsettling report in a statement Wednesday.

“We are strengthening prevention, promoting harm reduction, expanding treatment, and supporting people in recovery, as well as reducing the supply of harmful substances in our communities,” he said. “And we won’t let up. To all those families who have mourned a loved one and to all those people who are facing addiction or are in recovery: you are in our hearts, and you are not alone. Together, we will turn the tide on this epidemic.”