Supplementary Material for: Telephone-guided sleep restriction for insomnia: A randomized sleep diary-controlled trial

Introduction: Insomnia is common, but access to its first-line treatment, Cognitive Behavioral Therapy for Insomnia (CBT-I), is limited. To explore a scalable alternative, we investigated the efficacy of Sleep Restriction Therapy (SRT), a core component of CBT-I, delivered via telephone.
Methods: In a randomized controlled trial, 147 adults with insomnia were allocated to 6 weeks of telephone-guided SRT (n = 76) or a sleep diary control group (n = 71). The SRT group received weekly supporting phone calls lasting 10 to 15 minutes. At baseline and post-test, we measured insomnia severity (primary outcome), sleep diary measures, anxiety symptoms, depressive symptoms, pre-sleep arousal, sleep-safety behaviors, daytime sleepiness, and dysfunctional sleep-related cognitions (secondary outcomes). The SRT group repeated these measures at 3- and 6-month follow-up.
Results: Telephone-guided SRT showed large between-group effects on insomnia severity at post-test relative to the sleep diary control group (d = 1.52; p < .001). Based on intention-to-treat, 36 (47%) participants randomized to SRT achieved clinical improvement, and 23 (30%) achieved insomnia remission. We found medium-to-large between-group effects at post-test (d = 0.53 to 1.18) for all secondary outcomes except daytime sleepiness and total sleep time. At 3- and 6-month follow-up, the primary and all secondary outcomes, including daytime sleepiness and total sleep time, improved relative to baseline within the SRT group (d = 0.50 to 1.93).
Conclusion: This trial shows that telephone-guided SRT is an effective insomnia treatment requiring minimal therapist guidance. If direct comparisons with CBT-I corroborate these findings, SRT could be an interesting scalable alternative to CBT-I as a first-line insomnia treatment. Trial registry: NCT05548907