The first overdose death of a Riverside County resident from carfentanil was confirmed on Thursday by county health officials.
The synthetic opioid is 100 times stronger than fentanyl and 10,000 times more potent than morphine, they said.
The local resident, a man in his 40s, fatally overdosed on carfentanil in March 2025 outside of Riverside County, according to a news release from Riverside University Health System. They did not say where the death occurred or under what circumstances.
Health officials said it can take months to confirm a cause of death, particularly if it occurs outside the county.
Carfentanil is typically used to tranquilize elephants and other large animals, according to the Drug Enforcement Administration.
The drug is extremely potent. About two milligrams of regular fentanyl is enough to kill a human.
“Any exposure to carfentanil is potentially life-threatening,” Sean Nordt, a doctor at Loma Linda University Health, said in an interview.
“There are chemical properties to carfentanil that make it bind more, [it has] a tighter binding to the opioid receptor,” he said. That’s why carfentanil lasts about six hours, compared to the 45 minutes fentanyl typically lasts.
Administering naloxone can reverse a carfentanil overdose, though multiple doses may be required. Naloxone is available to purchase over the counter at drug stores.
“Every life lost from opioids is one too many,” Riverside County Public Health Officer Dr. Jennifer Chevinsky said in the release. “Together, we can continue to raise awareness about the risks associated with drug use and work as a community to support safety, reduce harm and care for one another.”
Overdose deaths involving carfentanil increased across the U.S. from 29 in January – June 2023 to 238 in the same period in 2024, the Centers for Disease Control and Prevention said.
However, the number of total opioid overdose deaths declined nationally by 27% in 2024 compared to the previous year, according to the CDC. Locally in Riverside County, opioid overdose deaths were down 25% in 2024, Riverside County health officials said.
Carfentanil entered the U.S.’s illegal drug trade in 2013 as an additive to or replacement for white powder heroin in the Northeast, according to the CDC.
