Background: Recreational marijuana use is rising, especially among young adults. The cardiovascular (CVD) effect of marijuana remains mostly unknown.Methods: This is a retrospective study of 14,490 patients admitted to our hospital between 2012 and 2014 who had urine toxicology done for various reasons. Patients with a primary diagnosis of acute coronary syndrome (ACS) were queried in both the marijuana-positive group (n = 59) and the marijuana-negative group (n = 195). The risks of having ACS were compared in both groups.Results: There was no difference in the risk of having ACS between the two groups in the population < 54 years of age (OR: 0.90, 95% CI: 0.67-1.20, p = 0.48). However, there was a significant difference in the risk of having ACS in the 18-36 age group (OR: 2.84, 95% CI: 1.14-7.07, p = 0.01). Multivariate analysis performed to adjust for the potential confounding effects of smoking and cocaine use showed that marijuana use (OR: 0.93, 95% CI: 0.68-1.25, p = 0.65) did not increase the likelihood of ACS for patients ≤ 54 years or for those in the 37-54 age group (OR: 1.11, 95% CI: 0.79-1.53, p = 0.50). However, among the 18-36 age bracket, marijuana use was independently associated with a higher risk of ACS (OR: 5.24, 95% CI: 1.84-16.93, p = 0.002). Conclusion:In younger patients (age 18-36 years), marijuana use is independently associated with a fivefold higher risk of ACS.