Abstract:Objective: To study the prevalence of alcohol and substance use among medical students. Material and Methods: A cross-sectional study surveyed Prince of Songkla University medical students in 2016. Questionnaires for demographic data, the Alcohol Use Disorder Identification Test (AUDIT), experience with alcohol and substance abuse, and the Patient Health Questionnaire-9 Thai version (PHQ-9) were used. We analyzed the data in order to describe the behavior of subjects by descriptive statistics. The factors associated with alcohol used were analyzed by chi-square test and logistic regression. Results: Seven hundred thirty-nine (70.1%) of medical students completed the questionnaires. Participants, 56.0% were female and 44.0% were male. Mean age was 21.2 years old; 53.3% have drunk alcohol; the gender proportion of drinkers was 60.0% of males and 48.1% of females. By AUDIT, 23.1% of medical students were high-risk drinkers. The most common reason for alcohol consumption was social engagement (91.9%) and the most common reason for not drinking was having knowledge about the harmful health effects of alcohol (51.2%). Of the medical students, 7.6% had experience with substance use. The drugs most commonly used were cigarettes (5.3%) and baraku (4.6%). According to the PHQ-9, 11.2% of all medical students, 12.6% in males and 10.1% in females had depression. However, these high levels of depression did not associate with a high-risk of alcohol consumption. The significant factors that associated with high-risk drinking were gender [odd ratio (OR)=1.9 (1.1-3.4)] and experience with substance use [OR=3.8 (2.0-7.3)]. Conclusion: Half of medical students drank alcohol and approximate 1 in 10 had experience with substance use. Gender and experience with substance use were the significant factors that correlated with high-risk drinking.