Marijuana abuse continues to plague society and the lack of effective treatments warrants concern. Catalytic antibodies capable of oxidatively degrading the major psychoactive component of marijuana, Delta(9)-tetrahydrocannabinol (Delta(9)-THC), are presented. The antibodies generate reactive oxygen species from singlet oxygen (O-1(2)*), using riboflavin (vitamin B-2) and visible light as the O-1(2)* source. Cannabitriol was identified as the major degradation product of this reaction, demonstrating the ability of an antibody to catalyze a complex chemical transformation with therapeutic implications for treating marijuana abuse.