Carfentanil, a more potent form of fentanyl, is contributing to overdose deaths in the U.S., the Centers for Disease Control and Prevention (CDC) says in a new report.

Carfentanil was detected in 513 overdose deaths between 2021 and early 2024, the CDC found. It is designed to tranquilize large animals and is estimated to be 100 times stronger than fentanyl, according to The Hill. Just 2 milligrams of carfentanil can tranquilize an elephant; that same amount can kill 50 people, according to the Department of Veterans Affairs.

The CDC report noted that approximately 70% of U.S. overdose deaths in 2023 were estimated to involve illegally manufactured fentanyls (IMFs). Although rare, deaths with carfentanil detected increased approximately sevenfold, from 29 during January–June 2023 to 238 during January–June 2024; 37 states reported carfentanil detection.

According to the CDC, overdose prevention efforts that address widespread presence of IMFs, including carfentanil, and can rapidly adapt to other potent opioids in the drug supply, might result in lasting reductions in overdose deaths across the United States.