Self-guided online cognitive behavioural therapy for insomnia: A naturalistic evaluation in patients with potential psychiatric comorbidities.

•Unguided iCBT-I produced significant improvements in participants’ insomnia symptom severity, psychological distress, and general wellbeing.•65% of participants who reported pre-treatment insomnia severity at clinical levels remitted following treatment with unguided iCBT-I.•Adherence to the iCBT-I program was markedly higher than other unguided iCBT programs when accessed in naturalistic settings.•Unguided iCBT-I can be successfully disseminated to the public in a naturalistic setting.