"This is poison": Inside fentanyl's mounting death toll

In New York City, the majority of autopsies of overdose deaths now reveal that fentanyl was involved, including that of Michael K. Williams, the actor found dead in his Brooklyn apartment.

It is spliced into party drugs where it can be consumed unwittingly, as it was by six people killed by a single batch of laced cocaine on Long Island this summer.

While the mounting deaths show the devastating consequence of fentanyl’s seep, it is less widely understood why the drug has mushroomed. And why so many illicit products — from fentanyl-laced cocaine and crystal methamphetamines, to marijuana sprayed with fentanyl, to faux prescription pills that are in fact fentanyl, colored and stamped to resemble a brand-name drug — now contain it.

The spread of fentanyl has been stealthy, steady and deadly, according to interviews with nine people involved in the sale of illegal drugs in New York, where much of the country’s fentanyl enters the street market, as well as law enforcement and addiction experts. The identities and backgrounds of the nine people were confirmed by The Times through their criminal records, lawyers and addiction counselors.