MINEOLA, N.Y. (CBSNewYork) — Use of the dangerous drug fentanyl is on the rise on Long Island and causing a large amount of overdoses.

Forty-two people have died from fentanyl-related overdoses in the past 15 months, the highest death rate Long Island has seen in a decade, WCBS 880’s Sophia Hall reported.

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“To give you a sense, it’s 50 to 100 times stronger than morphine and about 50 times more powerful than heroin,” said Dr. Jeffrey Reynolds from the Long Island Council on Alcoholism and Drug Dependence.

Reynolds said dealers are mixing fentanyl with heroin to give users a greater high.

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“Fentanyl has a lag time of about 20 to 25 minutes,” Reynolds said. “Heroin users expect an almost immediate reaction, and when they don’t get that immediate reaction, they think, ‘Well, this is just lousy heroin. I should take more.’ And then 20 to 25 minutes later, the strength of that fentanyl kicks in, and that’s where we see a lot of overdoses.”