The clinical effects of sleep restriction therapy for insomnia: A meta-analysis of randomised controlled trials.

Sleep restriction therapy (SRT) is an established treatment for insomnia that has been used in clinical practise for over 30 y. It is commonly delivered as part of multicomponent cognitive-behavioural therapy (CBT-I) but has also been linked to beneficial effects as a standalone intervention. In order to quantify the efficacy of SRT we performed a comprehensive meta-analysis of randomised controlled trials (RCTs) comparing SRT to minimally active or non-active control groups. Primary outcomes were self-reported insomnia severity and sleep diary metrics at post-treatment. Weighted effect sizes were calculated with Hedges' g and risk of bias was assessed by two independent raters with the Cochrane tool. Our search yielded eight RCTs meeting inclusion/exclusion criteria. Random effects models revealed large treatment effects in favour of SRT versus control for insomnia severity measured with the insomnia severity index (g = -0.93; 95% CI = -1.15, -0.71), sleep efficiency (g = 0.91; 95% CI = 0.52, 1.31), sleep onset latency (g = -0.62; 95% CI = -0.84, -0.40), and wake-time after sleep onset (g = -0.83; 95% CI = -1.11, -0.55). No effects were found for total sleep time (g = 0.02; 95% CI = -0.29, 0.34). Results should be interpreted in the context of the small number of comparisons (≤6 per outcome), high risk of bias (6 out of 8 studies met criteria for high risk), and heterogeneity in study design and SRT administration. Only a small number of studies provided outcomes at follow-up (n ≤ 3), hindering assessment of long-term effects. Sleep restriction therapy effectively improves insomnia severity and sleep continuity in the short term; more studies are needed to assess if effects are sustained at long-term follow-up (>3 m). Post-treatment effect sizes appear as large as multicomponent CBT-I. To reduce risk of bias, future studies should consider testing the effects of SRT against control groups that are matched for non-specific treatment effects. Large-scale pragmatic trials are also needed to test if SRT is effective in clinical practise and to quantify effects on daytime functioning and quality of life.