Abstract This paper analyses the extent of influence of personality issues on the effectiveness of substance abuse preventive measures among secondary students in Kakamega County through cross sectional survey design. The study was guided by social cognitive theory. The target population was 59675 form three students, 1080 class teachers, 530 G/C teachers and 12 sub-county directors of education in the study area. Multi-stage sampling, simple random and purposive sampling techniques were use...