Circadian misalignment and reduced rest-activity amplitude are candidate phenotypes in insomnia disorder, warranting phenotype-stratified trials of circadian interventions.

This narrative review proposes that some insomnia patients have circadian misalignment, reduced rest-activity amplitude, increased sleep-timing variability, or abnormal light exposure, which may require circadian-targeted adjunctive treatments. It suggests a phenotyping framework combining sleep diaries, actigraphy, light exposure, DLMO, and core body temperature to distinguish CRSWD-dominant insomnia, insomnia with circadian modifiers, and comorbid insomnia and CRSWD. CBT-I remains first-line, with fixed wake time, morning light, evening light restriction, timed low-dose melatonin, and scheduled activity as candidate adjunctive modules for future phenotype-stratified trials.