California Marijuana Law Complicates Intoxication Defense in Work Injury Claims

California’s legal landscape around marijuana use continues to evolve, creating new challenges for insurance claims adjusters evaluating intoxication defenses in workplace injury cases. Despite the legalization of recreational cannabis under Proposition 64 and medical use allowances, marijuana remains illegal under federal law, which keeps the door open for using intoxication as a defense in workers’ compensation (WC) claims—if the right evidence exists.

Attorney Donald Barthel details the burden placed on the defense: not only must they prove the worker was intoxicated, but they also need to establish that the intoxication directly caused the injury. This two-pronged standard remains firmly in place under Labor Code 3600(a)(4), but proving impairment from marijuana is uniquely difficult. THC can linger in the system long after any effects have worn off, meaning a positive drug test alone often fails to meet the legal threshold.

This issue became even murkier after the enactment of Assembly Bill 2188 in 2024. The law prevents employers from taking adverse action based on drug tests detecting non-psychoactive cannabis metabolites. As a result, claims defenses can no longer rely on standard urine tests as proof of impairment. Instead, employers and adjusters must turn to more resource-intensive methods—blood tests for active THC, witness testimony about visible impairment, and expert toxicology opinions—to link cannabis use to workplace accidents.

For claims professionals, the key takeaway is clear: defending claims on marijuana use now demands a far more rigorous evidentiary approach. Adjusters should be prepared to dig deeper for contemporaneous behavioral evidence and seek expert guidance to build a viable intoxication defense.