The Lowell Fire Department on Thursday warned of what appears to be "a lethal batch of opiates" in the area, after four fatal overdoses in 12 hours.
In a release posted to Facebook and Twitter, Chief Jeffrey Winward said the department believes the overdoses resulted from "a mix of heroin-fentanyl and cocaine-fentanyl."
He's warning users to be extra vigilant and is encouraging anyone who wants help to contact the department.
"This is the first time we've had this many [fatalities] in a short time but we have put out a few other warnings in the past and they have worked," Winward told WBUR. "People have heeded our warnings, and we hope they do the same this time"
The powerful synthetic opioid fentanyl was present in 83 percent of overdose deaths in Massachusetts in 2017.