Updated June 18.
Preliminary numbers show California's overdose deaths from the synthetic opioid fentanyl increased by 57% in 2017, according to the state's Opioid Overdose Surveillance Dashboard.
Fentanyl overdoses claimed 373 Californians, according to the Dashboard, an online tool that gathers data from the California Department of Public Health, the Office of Statewide Health Planning and Development, and the Controlled Substance Utilization Review and Evaluation System.
Fentanyl is up to 50 times more powerful than heroin and can be 100 times more potent than morphine. It's often added to other street drugs, and can overwhelm and kill someone who has no tolerance.
The number of overdose deaths last year could rise, however, according to Dr. Phillip Coffin of the San Francisco Department of Public Health. He said determinations on causes of death are still being closed in some 2017 cases.