Objective: This study was designed to examine the relationship between personality traits and substance use among college students in Tehran.

Materials & Methods: This was a correlational prediction study. Subjects were 914 bachelors or masters students with a mean age of 23.13 years, selected from one of Tehran’s universities through cluster sampling. The ‘Big Five Inventory’ (Goldberg, 1999) and risk behaviors questionnaire (National College Health Risk Behavior Survey, 2007) were used to collect data. The criterion or dependent variable was ‘substance use’ and ‘personality traits’ was the predictor or independent variable. Data was analyzed through multiple regression analysis.

Results: Substance use had a positive correlation with ‘Agreeableness’ and ‘Openness’ and a negative correlation with ‘Extraversion’, ‘Consciousness’ and ‘Emotional Stability’. ‘Consciousness’, ‘Agreeableness’, ‘Emotional Stability’ and ‘Openness’ were important variables in prediction of substance use. This regression model can explain 30% of the total variance of substance use score.

Conclusion: Results of this research indicate that personality variables are determinant factors of substance use. Likewise, with the possibility of prediction of substance use based upon personality traits, we can identify at risk individuals and focus on preventive interventions.