Patterns and Correlates of Co-occurring Smoking, Alcohol Use, Gambling, and High Internet Use Among University Students: A Cross-Sectional Study in Türkiye.

University life may facilitate multiple addictive behaviors that tend to cluster rather than occur in isolation. The aim of this study was to estimate the prevalence and co-occurrence patterns of daily cigarette smoking, past-30-day alcohol use, gambling, and high daily internet use, and to evaluate their sociodemographic and behavioral associations among undergraduate students in Türkiye. This cross-sectional study was conducted at Inonu University (Malatya, Türkiye) between February-May 2024. Using stratified random sampling, n = 366 students were included. Outcomes were daily smoking, past-30-day alcohol use, past-year gambling, and high daily internet use (≥ 5 h/day). Analysis included UpSet framework for co-occurrence and logistic regression models. A Firth-penalized model assessed smoking factors. Prevalence was 39.1% for high internet use, 30.1% for daily smoking, 22.1% for gambling, and 7.7% for alcohol use. Overall, 59.0% reported at least one behavior, 27.6% reported ≥ 2, and 10.4% reported ≥ 3; the most common triple combination was high internet use, smoking, and gambling (6.3%). Male sex was associated with smoking (adjusted odds ratio [aOR] = 3.19) and gambling (aOR = 5.95). Smoking was independently associated with alcohol use (aOR = 5.34) and gambling (aOR = 2.25). High internet use was associated with highest family income (aOR = 2.81), alcohol (aOR = 2.54), and gambling (aOR = 2.73). Peer smoking showed an association with daily smoking (aOR = 17.25 for 2-3 friends vs. none). Risk behaviors are common and frequently cluster, particularly internet use, smoking, and gambling. These findings support integrated campus prevention and screening strategies that address multiple behaviors simultaneously rather than in isolation.