Drug and substance abuse is a global concern and Kenya is no exception to this issue. Various parties, including teachers, parents, church officials, and other stakeholders, have been actively engaging in seeking to understand its underlying causes and the effect to academic performance. Hence there is a pressing need to address this problem. This study aimed at investigating the effect of drug and substance abuse on the academic performance of secondary students in Thika West Sub-County, Kiambu county. The study used descriptive survey research design. The study used interview and questionnaires to gather data. Interviews were set to collect information from principals and guidance and counseling teachers. Questionnaires were given to the students patterning questions with the aim of collecting data. Qualitative analysis was used to analyze the information gathered.