While time in bed restriction is a core treatment mechanism of Sleep Restriction Therapy (SRT), empirical research has not yielded a relationship between insomnia improvement and adherence to the prescribed time in bed. We coin this discrepancy the adherence conundrum of SRT. Understanding this adherence conundrum is clinically important, as stringent time in bed restriction makes SRT particularly demanding for patients. We propose that one important aspect has been overlooked in adherence studies and could potentially obscure an adherence-effect relationship: the achieved dose of time in bed restriction. To explore this possibility, we conducted a secondary analysis of a randomised controlled trial in which adults with insomnia received 6 weeks of SRT (N = 54). As did previous studies, we found that adherence to the prescribed time in bed did not predict insomnia severity, β = -0.03, t = 1.66, p = 0.10. Contrary to expectations, controlling for achieved dose did not alter this finding, β = -0.03, t = 1.48, p = 0.14. As most participants achieved a large dose of time in bed restriction, a ceiling effect may be operating, beyond which adherence may offer little incremental benefit. We call for research into the adherence conundrum and the optimal prescribed time in bed that balances tolerability and efficacy. Such research will be essential to guiding how strictly the rules of SRT need to be enforced in clinical practice. Trial Registration: Sleep Restriction Treatment for Insomnia. https://clinicaltrials.gov/study/NCT05548907.
Looman et al. (Wed,) studied this question.