Aim: The aim of this research is to investigate the relationship between rational drug use and healthy lifestyle behaviours of university students. Method: This descriptive and cross-sectional study consisted of 1115 students from a university in the Southeast-East Anatolia Region in the autumn semester of the 2019–2020 academic year. In the collection of data, ‘Student Introduction Form’, ‘The Rational Drug Use Scale’ and ‘The Health-Promoting Lifestyle Profile II’ were used. Ethical approval was obtained from the Batman University Ethics Committee. In addition, necessary legal permissions were obtained from the institution where the study was conducted and from the students. Descriptive statistics, number, percentage, independent t-test, ANOVA test and Spearman’s rank correlation were used in the Statistical Package for Social Science (SPSS) 22.0 package software to analyse the data. Results: The average age of the students was 21.31 ± 2.37 years, and their monthly drug expenditure was 142.63 ± 157.200 Turkish Lira. Some 28.1% of them were third-year students, 59% had graduated from Anatolian high school, 59.6% were living with their nuclear family, 49.1% had an equal level of income and expenditure, 7.7% had no chronic disease, and 9% had regular medication. Some 57.8% of them had health insurance. The Health-Promoting Lifestyle Profile II scale mean score of the students was 124.12 ± 21.37 and the Rational Drug Use Scale mean score was 33.65 ± 6.75. A statistically significant difference was found between the students’ class, income, and the total mean scores of the health-promoting lifestyle profile II scale ( p < 0.05). A statistically significant difference was found between the school type, family type and income status of the students and the total mean scores of the rational drug use scale ( p < 0.05). Conclusion: A strong positive correlation was found between rational drug use scale and the health-promoting lifestyle profile II scales.