Law enforcement agencies across Maryland have launched a joint investigation to find the source of a deadly variant of heroin that has claimed dozens of lives in recent months and sent outreach workers scrambling to warn addicts.

Authorities say the powerful mixture of heroin and the synthetic opiate fentanyl has also turned up in New England, New York and Pennsylvania. In Maryland, they say, they have been caught off guard by the scale of the problem.

For months, health workers, drug users and police have caught glimpses of the cocktail and the damage it has caused. The scope of the carnage came into focus last week, when the chief medical examiner's office announced that the mixture had been linked to 37 Maryland overdose deaths since September.

The deaths are scattered across the state with a concentration in the Baltimore area, and Maryland State Police reported seizures of the combination in Wicomico County, Frederick and Hagerstown.

The federal Drug Enforcement Administration, the state police and other agencies will meet Friday to work out how to track down the source of the fentanyl, and plot a strategy to take manufacturers and distributors of the drug off the street.

New drug combinations — often emanating from illegal labs in California or Mexico and sold under names such as Theraflu and Bud Ice — sweep through the Midwest and the East Coast every few years.

The latest wave has also been tied to deaths in New York, Pennsylvania and Rhode Island.

"We've been watching out for this," said Chris Serio, who directs Baltimore's needle exchange program. State officials say Baltimore has seen 10 fentanyl-linked deaths, the largest number in the state.

Users report that the powdery mix looks whiter than regular heroin, Serio said, but some might not even know that they are shooting up a particularly dangerous cocktail.

"It's going to feel like it's just potent heroin," said Gary Tuggle, the head of the Baltimore DEA office. "True heroin addicts, when they find something that's potent on the streets, they tend to gravitate towards it."

That leaves law enforcement officials in a bind. They want to warn heroin users to stay away from fentanyl, but they also worry that publicizing brand names and types of packaging will actually lure users.

Jacqueline Robarge, executive director of Power Inside, a group that serves vulnerable women, said drug users are an educated crowd who should be trusted to make informed decisions.

"It is an emergency, in terms of people needing to know about this specific threat," Robarge said. She drafted a flier Tuesday to warn users of the danger and suggest precautions.

"We want you to stay alive!" it reads in part. "Do a tester shot. Don't use alone."

Tracking the source of the fentanyl could be difficult. Authorities are moving quickly to act, and will plot their next moves at the meeting Friday.

"The goal is to try and identify where the fentanyl is being introduced into the heroin," U.S. Attorney Rod J. Rosenstein said.

Assistant State's Attorney Tony Gioia, said investigators will have their work cut out for them. As a defense attorney in the early 1990s, Gioia represented a member of a crew accused of selling fentanyl in Baltimore.

"Finding an illicit fentanyl lab can be like finding a needle in a haystack," he said. "Very few drug organizations will actually know where the lab is located. You do not need a large warehouse, but you need someone with a solid background in organic chemistry."

Gioia said the 1990s case centered on a crew working around Mondawmin Mall. He said police worked informants and obtained wiretaps to build their case.

Federal officials say they have several ways to pursue manufacturers and distributors.