Purpose: Medical students are at increased risk of poor mental health and need to regularly engage in preventive programs to maintain well-being. However, many do not and it remains an open question whether these programs should be mandatory. We implemented a RCT to examine the effectiveness of assigning medical students to a wellness intervention on adherence to engagement in the assigned intervention and on psychological and academic outcomes. Method: Medical students participated in a 12-week randomized controlled intervention involving one-hour wellness sessions of either (1) yoga; (2) mindfulness; or (3) walking, held twice-weekly. Students completed standardized psychological assessments at baseline and following the intervention. Results: Students randomized to the wellness intervention group engaged in more minutes of assigned activities than students randomized to the control. There was a significant difference in the change from pre-to post-intervention on measures of state anxiety and perceived stress, with better outcomes for the intervention group. Conclusions: The assignment of twice-weekly wellness intervention sessions protects medical students from state anxiety and perceived stress with no negative impact on academic performance. Students adhered to the sessions and reported enjoying the sessions once trying them. Actual engagement is more important than wellness activity type.