I need an insight on whether can "alcohol use" be measured as a mediator between the negative relationship of stress and academic performance among University students.
Long answer: In fact, health/-coping behaviours, such as alcohol consumption, are commonly taken as intermediate variables of stress.
However, keep in mind that the causal direction of your assumed process could also be reverse, e.g., when having good performance causes reduction in stress, and reduced stress and good performances may increase alcohol consumption.