INTRODUCTION: The impact of marijuana use has become a national topic with the increase in state’s legalizing or decriminalizing the use of the drug. To understand the impact this new trend may have on the population, it is necessary to characterize the interaction between marijuana use and health outcomes. Previous research has focused on the acute effects of marijuana on mental health and longitudinal impacts of marijuana use in the adolescent population. However there are no previously published studies on the impact of early onset marijuana use on adult mental health. AIM: This study aims to determine the prevalence of early onset marijuana use and if there is a statically significant association between early onset marijuana use (<14 years old) and increased prevalence of adverse mental health outcomes in adult life. METHODS: This study was conducted using data from the 2014 National Survey on Drug Use and Health. The study population included 41, 285 participants 18 or older at the time of the cross-sectional survey. Adult mental health outcomes were modeled for both early onset marijuana users and non-early onset marijuana users using a multiple logistic regression model to calculate both adjusted and unadjusted odds ratios (AOR’s, OR’s) with 95% confidence intervals. Statistical analysis was performed to examine the association between early onset marijuana use and negative adult mental health outcomes including serious mental illness, any mental illness and lifetime depressive episodes. RESULTS: This study found that in adults aged 18 and older the prevalence of early onset marijuana use was 8.3%. The prevalence of early onset marijuana use varies by gender, with a prevalence of 5.1(95% CI 4.7-5.2) for males and 3.3(95% CI 3.1-3.5) for females. Early onset marijuana use had a statistically significant association with all three indicators of poor adult mental health. The AOR for early onset marijuana use and serious mental illness was 2.3(95% CI 1.972-2.758). The association between early onset marijuana use and adult depressive episode had an AOR of 2.1(95% CI1.906-2.389). DISCUSSION: These findings suggest that early onset marijuana use is a risk factor for adverse mental health outcomes in adulthood. Consistent with findings from other nationally representative surveys, the prevalence of early onset marijuana use is higher in males than females. Early onset marijuana use is associated with increased odds of past year serious mental illness and past year any mental illness. This suggests that legislature considering marijuana legalization must also consider policies addressing under age use of the drug. Further longitudinal research is needed to father assess the association between early onset marijuana use and adult mental health.