Low adherence in self-guided internet interventions is linked to poorer outcomes. Although some predictors of adherence have been identified, few are modifiable for widespread application. One personal variable with the potential to increase adherence in internet interventions is context-specific self-efficacy. This protocol outlines a randomized controlled trial design, divided into two phases. In Phase 1 (students, N = 216), participants will complete a self-efficacy-enhancing exercise, which will be compared to a waitlist control group to test its effectiveness in increasing internet intervention adherence self-efficacy. Phase 2 will be the main two-arm trial, where all participants (medical students, N = 952) will undergo an internet intervention called Med-Stress Student. In the experimental group, the program will be preceded by the self-efficacy-enhancing exercise developed in Phase 1. We anticipate that participants in the experimental group will show higher adherence (primary outcome) to the intervention and greater improvement in intervention outcomes (secondary outcomes i.e., lower stress and higher work engagement) at posttest, as well as at six-month and one-year follow-ups. If effective, enhancing context-specific self-efficacy could be recommended before any internet intervention as a relatively simple way to boost participants' adherence.