Massachusetts Attorney General Maura Healey is introducing legislation to increase the penalty for trafficking the painkiller Fentanyl. Healey says the substance is often added to heroin without the user knowing to increase the high, and make the combination more addictive.

“Like so many users out there, they think they’re using heroin,” Healey says. “What they’re getting actually is not heroin but something that is even more potent, more deadly, more lethal than ever, and that’s exactly why we’re taking this step today.”

The new law would lower the amount needed to prosecute trafficking charges against drug dealers, while increasing the maximum sentence to 20 years in state prison.

The Massachusetts State Police says the amount of Fentanyl turning up in drug samples has skyrocketed in the last 2 years–from 5 to more than 400 so far this year.

Correction: An earlier headline on this story said “tracking” instead of “trafficking.”