ABSTRACT Problems with initiating and maintaining sleep are among the most common health complaints, with prevalence rates exceeding 50% depending on the survey. Preventing the progression to chronic insomnia may reduce public healthcare costs and prevent secondary illnesses. This study examined the effectiveness of a novel app‐based digital course using cognitive behavioural therapy for insomnia (CBT‐I) in preventing the manifestation of insomnia among individuals with sub‐threshold to moderate symptoms. Participants were assigned to an intervention group ( N = 191, ages 20–75) or a waitlist control group ( N = 72, ages 22–77) and assessed at three time points: Pre‐intervention (T0), Post‐intervention (T1, after 7‐week course) and Follow‐up (T2, 3 months after course initiation) using the Insomnia Severity Index (ISI), Sleep Hygiene Index (SHI) and sleep diary entries. Results showed a significant reduction in insomnia severity (−4.8 ± 3.7 ISI points) and improved sleep hygiene (−3.5 ± 4.5 SHI points) from T0 to T1 ( d = 1.35, and d = 0.69, respectively), with stable effects maintained at the 3‐month follow‐up. Remission was achieved by 48% of the intervention group compared to 18% of the control group. Improvements were also observed in sleep latency, sleep efficiency and reductions in nocturnal awakenings and wake time after sleep onset ( d = 0.25–0.71). Activating evening activates, napping, irregular bedtimes, uncomfortable sleep environment, perceived stress and rumination significantly reduced ( d = 0.16–0.59). Notably, 68% of users reported sustained improvements in their sleep. The findings indicate that various sleep hygiene behaviours can be effectively modified through an app‐based CBT ‐I intervention. Trial Registration: This study was pre‐registered at Open Science Framework https://osf.io/yj2va
Kater et al. (2025) studied this question.