Drug abuse has become an international phenomenon, a torn in the flesh of nations across the globe. It has been identified as one of the precarious vices; an impediment to the academic excellence of students of tertiary institutions; and a threat to the future of the Nigerian nation. The task of the paper was to interrogate the effects of drug abuse on the academic performance of students of selected tertiary institutions in Lagos, Nigeria. A quantitative method of data collection was employed to get the task of the paper done. The work adopted social learning theory as its theoretical framework. The study found peer group pressure, experimental curiosity, remedy for low self-esteem, poor parenting and influence of role models among others as root causes of drug abuse among students of tertiary institutions in Nigeria. The finding revealed that the rise of drug abuse among the students of higher institutions of learning in Nigeria is at an alarming rate; by implication, absenteeism from school activities, loss of memory, lack of seriousness in academic work, declining grades, increased potential for dropping out of school and suspension from school to mention a few are attributed to drug abuse. The study concluded by recommending a peer education intervention strategy, enactment of laws to discourage drug abuse, inclusion of mandatory drug education in all educational programs, constant monitoring of students by parents, and setting up of guidance and counselling offices across the campuses. Constant awareness programmes about the effects of drug abuse on academic achievement are also appropriate.