Police agencies in the region warned the public Tuesday about a spate of recent deaths that appear to stem from drug overdoses as investigators try to determine whether the cases are related.

Glens Falls Police have investigated four apparent overdose deaths over the past six weeks, while State Police are investigating one from over the weekend in Salem, and Hudson Falls Police had two suspected overdoses last week, one of which was fatal.

Glens Falls Police Deputy Chief Joseph Boisclair said the Glens Falls deaths did not appear to be related, or the result of one bad batch of heroin or other drug. But he said the high number had investigators looking for a potential tie between them, including whether the recent arrival in the region of marijuana laced with fentanyl, a synthetic opioid that is far more powerful than heroin, could be playing a role.

Glens Falls Police did not have statistics on overdose deaths in Glens Falls over the last few years, as lag time for toxicology tests makes it tough to compare. (One local police agency recently received toxicology results from the State Police Forensic Identification Center for a 2016 death.) But they said the number of deaths in a short period of time was highly unusual.

“It’s fair to say we’ve never had four in this short of a span,” Glens Falls Police Detective Lt. Peter Casertino said.

The Glens Falls fatalities occurred as Hudson Falls Police investigate what was believed to be an overdose death last week, which was followed by a call later the same day at a neighboring home where Narcan was used to reverse the effects of an overdose, Hudson Falls Police Chief Scott Gillis said.

“It took four doses of Narcan to reverse it,” Gillis said.

Gillis said fentanyl was determined to be the drug used by the person who survived, and toxicology tests are pending for the fatality.

The most recent suspected overdose death occurred last weekend when a young man in Salem was found dead, and State Police are investigating the circumstances of that case.

Boisclair, who headed the department’s narcotics investigations before his promotion to deputy chief late last year, said the department has received word from informants that marijuana-and-fentanyl has been available locally.

Police agencies in the Capital Region warned about the presence of fentanyl-laced marijuana last week after dealing with overdoses and seizing the drugs during an arrest. The concern is that marijuana users do not know about the potentially deadly addition to their weed.

Boisclair said local police are also seeing an increase in synthetic drugs that are originating in China, which are being used despite the fact that no one knows what compounds they contain.

“Basically, they don’t have any ideas what they are putting into their bodies,” he said.