This study aimed to investigate the efficacy of a Danish adaption of a transdiagnostic sleep and circadian intervention, combining cognitive behavioural therapy for insomnia with chronotherapy. A randomised controlled trial enrolling 88 outpatients with depression, attention deficit disorder, or bipolar disorder suffering from insomnia or circadian rhythm disorders was conducted. Patients with insomnia and/or circadian rhythm disorders were randomised to either an intervention group receiving six individual sessions of a transdiagnostic sleep and circadian intervention or a control group receiving sleep hygiene education at a single session. Primary outcome was sleep quality and insomnia severity. Secondary outcomes were well-being, personal recovery, work ability, perceived overall health, sleep efficiency, sleep onset latency, wake after sleep onset, nocturnal awakenings, and sleep medication consumption. Data were collected via validated questionnaires, actigraphy, and sleep diaries, with assessments at baseline, week 2, and 6; actigraphy and sleep diaries were recorded continuously over the 6-week period. The intervention group statistically significantly improved sleep quality (p < 0.001), reduced insomnia severity (p < 0.001), and increased well-being (p = 0.002), personal recovery (p = 0.037), work ability (p < 0.001), and perceived overall health (p = 0.004) from baseline to week 6 compared to the control group. Actigraphy and sleep diary analyses revealed no statistically significant differences between the groups. In conclusion, the transdiagnostic sleep and circadian intervention was effective for both patients with insomnia and circadian rhythm disorders comorbid with depression, attention deficit disorder, or bipolar disorder. It resulted in improved sleep quality, a reduction in insomnia, and enhanced well-being, personal recovery, work ability, and overall health perception.
