Psychoactive substance use presents both economic and psychological burden to the society at large with far reaching consequences. The prevalence and pattern of substance use have been studied extensively in many settings; however studies carried out in primary care centres which are usually the first contact of patients with health care giver are few. The level of risk for adverse effects of these psychoactive substances and treatment needs of such patients are usually not assessed. This study aimed to assess the prevalence and pattern of substance use, level of risk for drug related adverse effects and treatment needs for substance use disorders among patients attending a primary health care centre. METHODS: Patients were recruited using systematic random sampling at the waiting room of the primary health care centre, Okeilewo, Abeokuta. Psychoactive substance use, level of risk and treatment needs was assessed using the WHO ASSIST. The ASSIST was validated using criterion validity with the WHO CIDI WMH Version. RESULTS: Prevalence of psychoactive substance use among patients both lifetime and current(3months) were in the following order alcohol(51.7% lifetime, 17.9% current), sedatives (23.4% lifetime, 8.2% current), stimulants like kolanuts (12.6% lifetime, 5.1% current), tobacco (6.8% lifetime, 2.2% current), cannabis (2.5% lifetime, 0.9% current), opioids (0.3% lifetime, 0.3% current). Level of risk for the adverse effect of any drug was highest for alcohol (3.7%), sedatives (3.4%), stimulants (2.5%), tobacco (2.1%), cannabis (0.9%), and opioids (0.3%) in the following order. Level of risk for any substance was increased in males compared to females except for mild stimulants (females 2.9%, males 0.0%). Level of risk for any substance was increased among the singles except for sedatives which was increased among the married (4.5% married, 0.0% singles). There was low risk for amphetamine, hallucinogen, cocaine, heroine and inhalants use as prevalence of use was 0.0% for all substances highlighted. A large number of patients (90.8%) had low risk for any drug and needed only drug related education, 8.3% had moderate risk for any drug and needed brief intervention while 0.9% had high risk for any drug thus required intensive treatment. Multivariate logistic regression indicated that alcohol risk and sedative risk were both associated with male gender. CONCLUSION: The findings suggest that some level of risk for common psychoactive substances exist among patients visiting the primary health care centre thus policies implementing a form of intervention or treatment for patients are needed