Stroboscopic light stimulation in adults reporting depressive symptoms: Safety, tolerability, feasibility, and active-comparator development in a staged early-phase study

Stroboscopic light stimulation (SLS) is a candidate non-pharmacological intervention that induces transient visual and affective experiences, with potential application in depression. Before efficacy testing, clinical development requires safety, tolerability, and feasibility data. We report a staged, single-site programme in adults reporting depressive symptoms. Study 1 tested 11 SLS parameter sets for safety and tolerability. Study 2 assessed whether an active comparator reduced subjective visual effects while preserving session context. Study 3 randomised 84 participants to four weekly supervised 31-minute sessions of strobe-emphasis or wash-emphasis SLS. In Study 1, 31 participants were analysed; no severe adverse reactions occurred, mean discomfort was low (0.49/10), and the highest session-level upper 80% confidence limit was 1.13/10, well below the prespecified threshold. Study 2 supported within-participant experiential separation between the two SLS configurations in healthy adults. In Study 3, endpoint data were available for 70/84 randomised participants (83.3%): 39/42 assigned to strobe-emphasis and 31/42 assigned to wash-emphasis. Discomfort remained low, with no serious SLS-attributable adverse events. Both configurations produced visual phenomenology in the Study 3 target sample, and the phenomenological separation observed during Study 2 was not reproduced between groups in Study 3. The comparison estimates differences between two active SLS configurations, rather than SLS versus no stimulation. Exploratory depressive-symptom estimates were imprecise, limited by differential endpoint availability, and should inform endpoint selection and subsequent trial design rather than efficacy. Overall, the programme supports further controlled evaluation of supervised SLS while identifying experiential separation, retention, masking, and endpoint selection as priorities for the next trial.