Correlates of recent overdose among people who inject drugs in the San Diego/Tijuana border region

•Fentanyl is commonly found in heroin and other illicit drugs in North America.•Overdose was associated with use of powder heroin known as china white.•Most who used china white did not believe it contained fentanyl.•Those who believed china white contained fentanyl were less likely to use it.•Harm reduction measures like drug checking may help people avoid overdose.