A crowdsourced megastudy of 12 digital single-session interventions for depression in US adults.

Digital, self-guided, single-session interventions (SSIs) deliver structured psychological support within one interaction. Here we crowdsourced 66 diverse 10-min SSIs for depression and, with input from researchers and lived-experience experts, selected 11 for testing in a preregistered online randomized controlled trial (ClinicalTrials.gov ID: NCT06856668 ). US adults (N = 7,505) experiencing elevated depressive symptoms were randomly assigned to 1 of the 11 crowdsourced SSIs, a validated behavioural activation SSI (active comparator) or a control condition without intervention content. Nearly all SSIs improved psychological outcomes immediately after completion (d ≤ 0.37). However, only two SSIs significantly reduced depression at 4-week follow-up (d = 0.14 and 0.15). Unexpectedly, completing an SSI made participants feel less confident and less interested in making changes to overcome depression at 4 weeks, on average (d = 0.05). Future work should aim to leverage SSIs' immediate benefits to promote sustained behaviour change or service engagement.