This study aimed at investigating the effect of drug abuse on the academic performance of students in Thika Sub-County. The objectives of the study were to; determine the commonly abused drugs, establish the causes of drug abuse among students, and to establish measures put in place to curb drug abuse in schools. The study used the descriptive survey research design. The target population was 32 secondary schools in Thika sub-county. Simple random sampling technique was used to sample 11 secondary schools. Twelve form three students were sampled using class register from the 11 schools sampled. Eleven principals and 11 guidance and counseling teachers from each sampled school were used as respondents. A total sample size of 154 respondents was used. The study used questionnaires and interview schedule to collect primary data. Data collected was analyzed using descriptive statistics (graphs, pie- charts and frequency distribution table). The findings in this study will be useful to educational planners, administrators in formulating policies and will also be helpful to scholars in need of undertaking research in the same topic.