A new study found that over 80% of people in New York City who use substances tested positive for fentanyl, even though only 18% used it intentionally.

The study, conducted by researchers at the NYU School of Global Public Health, suggests that many people who inject substances, particularly heroin, may be unknowingly ingesting fentanyl, which is the most common substance linked to overdose deaths in New York City. This can increase their risk of overdose. However, research also indicates that some are aware and actively look for heroin mixed with fentanyl. People using fentanyl knowingly or unknowingly can build up a tolerance to it, requiring increasingly larger amounts and turning to stronger substances than heroin.

Courtney McKnight, clinical assistant professor of epidemiology at NYU and the study’s lead author, advocated for more funds and resources to be fueled into prevention programs around the city. “More support access to these programs are needed to further reduce overdose mortality.”