NEW YORK (CBSNewYork) — The Nassau County Medical Examiner’s Office is warning the public after several deaths initially thought to be linked to the abuse of heroin, were actually found to have involved the narcotic fentanyl.

The Forensic Toxicology Laboratory has analyzed evidence linked to two of the cases and said the substance contained fentanyl in combination with the banned antipyretic metamizole.

Fentanyl is a synthetic narcotic painkiller of extremely high potency, the medical examiner’s office said. The drug is about 100 times more potent than morphine, which is the active ingredient in heroin.

The medical examiner’s office said fentanyl is clinically used for the treatment of severe pain or the induction of anesthesia. Severe respiratory depression can occur with the use of fentanyl.

Metamizole, which has been banned for use in the United States since 1997, is similar in use to ibuprofen. The substance was banned due to the potential for the development of agranulocytosis, which is the failure of bone marrow to make enough white blood cells.

The medical examiner’s office says the deadly mix of substances is presumably being distributed as heroin and marked as “24K” in red ink.

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