BackgroundDigital mental health interventions (DMHIs) can help bridge the gap between the demand for mental health care and availability of treatment resources. The affordances of DMHIs have been proposed to overcome barriers to care such as accessibility, cost, and stigma. Despite these proposals, most evaluations of the DMHI focus on clinical effectiveness, with less consideration of users’ perspectives and experiences.ObjectiveWe conducted a pilot randomized controlled trial of “Overcoming Thoughts,” a web-based platform that uses cognitive and behavioral principles to address depression and anxiety. The “Overcoming Thoughts” platform included 2 brief interventions—cognitive restructuring and behavioral experimentation. Users accessed either a version that included asynchronous interactions with other users (“crowdsourced” platform) or a completely self-guided version (control condition). We aimed to understand the users’ perspectives and experiences by conducting a subset of interviews during the follow-up period of the trial.MethodsWe used purposive sampling to select a subset of trial participants based on group assignment (treatment and control) and symptom improvement (those who improved and those who did not on primary outcomes). We conducted semistructured interviews with 23 participants during the follow-up period that addressed acceptability, usability, and impact. We conducted a thematic analysis of the interviews until saturation was reached.ResultsA total of 8 major themes were identified: possible opportunities to expand the platform; improvements in mental health because of using the platform; increased self-reflection skills; platform being more helpful for certain situations or domains; implementation of skills into users’ lives, even without direct platform use; increased coping skills because of using the platform; repetitiveness of platform exercises; and use pattern. Although no differences in themes were found among groups based on improvement status (allPvalues >.05, ranging from.12 to.86), there were 4 themes that differed based on conditions (Pvalues from .01 to .046): helpfulness of self-reflection supported by an exercise summary (greater in control); aiding in slowing thoughts and feeling calmer (greater in control); overcoming patterns of avoidance (greater in control); and repetitiveness of content (greater in the intervention).ConclusionsWe identified the different benefits that users perceived from a novel DMHI and opportunities to improve the platform. Interestingly, we did not note any differences in themes between those who improved and those who did not, but we did find some differences between those who received the control and intervention versions of the platform. Future research should continue to investigate users’ experiences with DMHIs to better understand the complex dynamics of their use and outcomes.