We investigated the interaction between approach behaviours (measured through performance on a resource-gathering task) and self-reported global life stress to predict substance use. Our hypothesis that high levels of approach behaviour in combination with high life stress would predict elevated substance use was guided by the reinforcement sensitivity theory (Gray & McNaughton, ). Ninety-three young adult students (61 women and 32 men) completed a computerized resource-gathering task and questionnaires assessing global life stress and substance use. Consistent with the hypothesis, approach behaviour was positively related to substance use for individuals with high life stress. The findings suggest that person by environment interactions are useful in understanding substance use and we discuss how approach-motivated individuals may arrive at different substance use outcomes as a function of stressful contexts. Copyright (c) 2016 John Wiley & Sons, Ltd.