Introduction: psychoactive substances are chemicals that affect the nervous system and alter the activity in the brain. Such substances include alcohol and other illicit drugs. This research study aimed to determine the prevalence and pattern of psychoactive substance use among students at a government secondary school in Ilorin, Kwara State, Nigeria. Methods: this study adopts a cross-sectional descriptive survey design. A simple random sampling technique was used to select 104 students for an invitation to fill a semi-structured questionnaire after consenting to the informed consent. Correlational analyses were performed between social characteristics and the knowledge of the effects and prevalence of substance use. Results: thirty-three point seven percent (33.7) of students reported to use psychoactive substances, with alcohol and tramadol being the most consumed. Those aged 15-19 years were found to have a higher prevalence of substances use than other ages. There was an important knowledge of the social perspective and health effects of using such substances, but they persisted in their consumption. Age and school level were observed to have a statistically significant correlation with the knowledge of the effects of drug use. Conclusion: our study shows that the prevalence and pattern of psychoactive substance use among the students are high considering their level and age. The majority of the students knew about psychoactive substance use and its social and health effects. We, therefore, recommend a multi-stakeholder effort within the community to curtail drug use among young people.