Objective: Substance use peaks in emerging adulthood, with evidence suggesting that college-attending emerging adults have a higher rate of substance use than their non-college attending peers. More insight into the factors that might contribute to substance use among college-attending emerging adults is needed. The current study examined the moderating role of emotion reactivity in the link between perceived importance of reasons for not using substances and lifetime marijuana and alcohol use. Participants: 440 undergraduate students under the age of 21 (M = 18.67, 47.7% Male) from a large Midwestern university participated in the study. Methods Participants responded survey items assessing reasons for not using, lifetime marijuana and alcohol use, and emotion reactivity. Results: Emotion reactivity only moderated the link between reasons for not using alcohol (i.e., reasons related to self-control) and lifetime alcohol use. Conclusions: Future research on reasons for not using is warranted. Implications for preventative interventions are discussed.