Heroin Is Being Laced With a Terrifying New Substance: What to Know About Carfentanil

A drug so powerful that it's used to sedate elephants is finding a new, illicit use laced into heroin, potentially contributing to hundreds of overdoses in the last several weeks.

The drug, called Carfentanil, is a synthetic opioid so strong that just a few granules the size of grains of table salt can be lethal. Since mid-August, roughly 300 people in at least four states have overdosed on heroin linked to Carfentanil and the less powerful compound fentanyl.