The Denver Police Department seized a “significant amount” of the synthetic opioid fentanyl in a recent operation, the first time it appeared in a “brick-like form” in Denver.

Denverite reports that at least 26 people in Denver have died from fentanyl overdoses this year so far. That number was 17 in 2018.

“This newly identified form of the drug may pose a high risk of overdose and death because it can easily be mistaken for heroin,” the Denver Department of Public Health & Environment warned.

The department added that fentanyl overdoses can occur quicker and are more difficult to stop. The substance can appear in heroin and cocaine.

Colorado’s drug overdose deaths have been climbing for two decades, reaching nearly 600 in 2017. Synthetic opioid overdoses comprised almost 20% of the total.

Researchers found in 2017 that 70% of heroin users said prescription opioids played a role in their decision to use the deadlier substance. Last month, a state legislative committee approved multiple bills to ease people away from prescription opioids and provide treatment to those already addicted within the criminal justice system.

A 2018 proposal to study whether the state’s criminal laws prevented users of fentanyl and other synthetic opioids from seeking treatment died in committee.