Objective: Substance use continues to be major risk behaviour among youth, with consequent physical and /or mental health
complications.The current study aimed to establish the prevalence and associated factors of substance use among selected secondary
school students in Lagos. Method: This was a cross-sectional and descriptive study among selected secondary school students in
Lagos. Permission was obtained from appropriate school authorities; as well as consent from each participant.TheWHO Students’ Drug
Use Questionnaire which had been previously validated in the country was used to obtain the drug use information from the subjects.
Analysis of the data was conducted using Epi-info version 5. Results: A total of 402 students were studied - of whom 43.5% (n=175)
were males and 56.5% (n=227) females. The mean age was 15.9 years. 83.1% (n=334) lived with their parents, 7.6% (n=31) with their
relatives and 7.2% (n=29) with friends. The commonest substances used by the subjects were caffeine (kolanut and coffee), mild
analgesics (paracetamol and aspirin) and the antimalarials, most especially chloroquine with lifetime use prevalence rates of 85.7%,
73.8% and 65.7% respectively. Generally, the prevalence rates for lifetime use of the substances varied from 3.8% (n=14) for Heroin
and Cocaine to 85.7% (n=344) for psychostimulants; and for current use varying from 2% (n=8)to 56.5% (n= 213). For the so called
“gateway drugs”: alcohol and tobacco, their lifetime use prevalence rates were 9.2% (n=34) and 5.2% (n=19) while the lifetime use
prevalence rate for cannabis was 4.4% (n=16). In terms of gender, the prevalence rates for males were generally higher than for their
female counterparts except for antibiotics, analgesics, heroin and cocaine. Reasons for using substances included relief from stress,
43.5% (n=175), self medication to treat illness, 23.8% (n=96), and to stay awake at night to study, 14.9% (n=60). Conclusion:Substance
use was found to be prevalent among students in this study involving over-the-counter and socially acceptable substances as well as
the abuse of illicit substances. It is advocated that there is a need to review existing health educational programmes.