Drug abuse, formerly known as drug misuse, is the usage of particular substances to produce pleasant sensations in the brain. Globally, there are more than 190 million drug users, and the issue is growing alarmingly, particularly among young persons under 30. In the last few years, stakeholders attempting to address the drug and substance abuse problem have intensified their campaigns for the prevention and reduction of drug abuse among the youth. The specific efforts have come through the establishment of such agencies as NACADA and the formulation of the Drug Control Master Plan. However, despite the huge efforts and resources committed to the cause, a high prevalence and rising rates of drug and substance abuse have been reported in Kenya lately. This study sought to evaluate the adverse effects of illicit substance and drug misuse among secondary school students in Siaya Township Ward, Siaya County. The study objectives included evaluating the role of drug and substance abuse on absenteeism, assessing its effects on academic performance, and analyzing its influence on truancy and school dropout among learners. Descriptive survey design was adopted in the study. The target population included secondary school students who were drug addicts. Stratified random sampling technique was applied to select respondents, ensuring representation from various demographic groups. The sample size constituted 171 respondents, determined using Yamane's formula. Questionnaire was used to collect data, and ethical considerations were observed throughout the process. The collected data was analyzed using descriptive statistics, with findings presented in tables, graphs, and pie charts. The findings revealed that drug and substance abuse led to non-completion of assignments, frequent absenteeism, and poor academic performance due to lack of concentration and loss of interest in schoolwork. The discussion highlighted how suspensions and expulsions exacerbated the issue, leading to school dropout and increased risks of social, psychological, cognitive, and behavioral issues. The study concluded that drug and substance abuse significantly affects students' educational outcomes and overall well-being. Recommendations included: MOE should consider developing counseling and rehabilitation programs for youth, especially secondary school students, to address drug addiction and facilitate reintegration into society. School administrations should adopt supportive approaches, such as counseling students and their parents/guardians, instead of using corporal punishment, suspensions, or expulsions, which may increase absenteeism and engagement in criminal behavior. The community, through religious leaders, local administrations, parents, and guardians, should initiate programs to educate adolescents on the dangers of drug and substance abuse and encourage behavior change.