Up to 50 times more potent than heroin, the synthetic opioid fentanyl is becoming an increasingly prevalent street drug on the South Shore, including Marshfield, leaving a trail of death in its wake.

Marshfield Police Chief Phil Tavares said fentanyl is all police are seeing right now in controlled purchases, which they conduct to build cases against drug dealers.

“It’s a major problem. It’s what we suspect most people are overdosing on,” Tavares said. “All our controlled purchases of what is being sold as heroin is in fact fentanyl. It’s not heroin.”

He said it’s a trend police have been monitoring for a while. Part of the reason for fentanyl's popularity is that it is cheaper than heroin and more powerful, he said.

With that increased strength comes increased danger.

“It doesn’t take much. Just a small amount of fentanyl can kill you,” said Tim Desmond, a spokesman for the U.S. Drug Enforcement Administration’s New England field office. “A grain-of-salt amount for some people could kill them.”

When heroin is laced with fentanyl, it produces a more intense high, but is more likely to cause a fatal overdose.

“When someone is addicted to opiates, there’s not much you can say in regards to ‘don’t use fentanyl,’" said Joanne Peterson, founder and director of Learn to Cope, a support organization for families impacted by addiction. “When they go to a dealer, they don’t always know what they are getting, or in some cases may actually go seeking it.”

For those who are seeking heroin but are actually sold fentanyl, overdoses and death are more likely because fentanyl is much more potent, Tavares said. The dosage is different, too, he said.

“You’re not going to drink the same amount of vodka as you would beer,” he said.

It’s not uncommon, experts say, for addicts to flock to an area where there have been large numbers of overdoses. In many cases, the allure of a powerful high outweighs the risk of death in an opiate-addicted mind.

“It shows just how strong the addiction is that they’re willing to take a chance,” Desmond said. “It’s really nasty stuff. Addicts are seeking out locations where they’ve heard of overdose deaths and are actually coming to those areas. It shows how strong a disease it is.”

Tavares said he has observed that trend as well.

“People are looking for the best possible product no matter what they’re buying,” he said, later adding, ”People that are in the business of looking for illegal narcotics are looking for the best high they can get, the most potent high they can get, and unfortunately some of them are finding it, which has a bad outcome."

Originally introduced in the 1960s as a painkiller for cancer patients, fentanyl has become a widespread street drug in the past couple of years. Known as “China white,” the drug is often laced into batches of heroin or, less commonly, cut with starch and sold on its own.

More than half of the 1,379 confirmed opioid-related deaths in Massachusetts in 2015 screened positive for fentanyl, according to data the Department of Public Health released May 2. State health officials estimate an additional 147 deaths were linked to opioids in 2015, but toxicology results are unavailable for those cases.

In 2012 in Marshfield, there were four unintentional opioid overdose deaths. There were also four in 2013, six in 2014, and three in 2015, according to data from the DPH. The Office of the Chief Medical Examiner is still confirming additional cases from 2014 and 2015.

“The first-time inclusion of data on fentanyl allows us to have a more honest and transparent analysis of the rising trend of opioid-related deaths that have inundated the Commonwealth in recent years,” Secretary of Health and Human Services Marylou Sudders said in a statement. “We will continue to work on prevention and intervention efforts when it comes to heroin and other opioids to eradicate this epidemic.”

DEA investigations have revealed the drug and its raw ingredients are often imported from China from Mexican cartels, Desmond said. It’s also illicitly produced in clandestine labs in Mexico and the United States.

Last November, Massachusetts passed a law criminalizing trafficking in fentanyl. The law, authored by Attorney General Maura Healey, became effective in February. Under the new law, anyone caught trafficking more than 10 grams of the drug could face 20 years in prison.

While fentanyl is often mixed into batches of heroin, Peterson said she knows of a handful of recent cases in which families lost a loved one to a fentanyl overdose with no heroin present.

“I think anyone who knowingly sells fentanyl has to know they could kill that person,” Peterson said. “If you’re selling 100 percent pure fentanyl, if the person dies, you should be charged with murder.”

Reporter Hannah Sparks contributed to this report

— Gerry Tuoti is the Regional Newsbank Editor for GateHouse Media New England. Email him at gtuoti@wickedlocal.com or call him at 508-967-3137.