Probability of fentanyl adulteration in cocaine selectively decreases cocaine demand

Fentanyl-related, cocaine-overdose deaths have drastically increased, yet research on how people who use cocaine perceive fentanyl adulteration is limited. This study developed the novel Adulterated Cocaine Purchasing Task, a modification of the original Cocaine Purchasing Task, to quantify how people respond to fentanyl adulteration in cocaine. In the Adulterated Cocaine Purchasing Task, participants indicated how much cocaine they would purchase when cocaine had no (0%) versus some (10%) probability of fentanyl adulteration. Study aims were to (a) determine how possible fentanyl adulteration affects cocaine demand and (b) determine which individual characteristics predict continued demand for cocaine despite fentanyl adulteration. This Amazon Mechanical Turk study included self-reported cocaine purchasers (N = 64), who completed self-report questionnaires (demographics, substance use history, depression/posttraumatic stress disorder symptoms, fentanyl knowledge quiz), and the Adulterated Cocaine Purchasing Task. Results showed (a) that a greater probability of fentanyl adulteration (10%) lowered cocaine demand, but only for intensity (Q₀; amount of cocaine consumed when free; p < .001); (b) no effect on other demand indices (O_max, P_max, essential value, breakpoint); (c) significantly more zero responders with 10% probability of fentanyl adulteration than 0%, p < .001; and (d) that opioid couse, depression, age, posttraumatic stress disorder, fentanyl knowledge, and cocaine use severity did not moderate the relationship between fentanyl adulteration and intensity. Overall, fentanyl adulteration reduced cocaine demand but only for volume preferred at minimal cost, not general motivational drive for use, illustrating the dangerous insensitivity to toxic contamination. The internal validity of the paradigm provides proof-of-concept for this approach to identify individuals at risk from fentanyl-adulterated cocaine. (PsycInfo Database Record (c) 2026 APA, all rights reserved).