Co-occurring insomnia and symptoms of depression, anxiety, and stress pose difficult diagnostic and treatment decisions for clinicians. Cognitive Behavioural Therapy for Insomnia (CBTi) is the recommended first-line insomnia treatment, however symptoms of depression, anxiety and stress may reduce the effectiveness of CBTi. We examined the effect of low, moderate, and severe symptoms of depression, anxiety, and stress on insomnia improvements during CBTi.

We undertook a chart-review of 455 patients (67% Female, Age M = 51.7, SD = 15.6) attending an outpatient CBTi program. Sleep diaries and questionnaire measures of insomnia, depression, anxiety, and stress symptoms were completed at pre-treatment, post-treatment and three-month follow up. We examined 1) the effect of low, moderate, and severe symptoms of depression, anxiety, and stress before treatment on changes in sleep diary and questionnaire measures of insomnia during CBTi, and 2) changes in symptoms of depression, anxiety, and stress during CBTi.

Sleep diary and questionnaire measures of insomnia severity showed moderate-to-large improvements during CBTi (d = 0.5–2.7, all p ≤ 0.001), and were not moderated by levels of depression, anxiety or stress before treatment (all interactions p > 0.05). Symptoms of depression, anxiety, and stress improved by three-month follow-up (M improvement = 41–43%; CI = 28–54, Cohen's d = 0.4–0.7).

Symptoms of depression, anxiety, and stress do not impair the effectiveness of CBTi. Instead, CBTi was associated with moderate-to-large improvement of depression, anxiety, and stress symptoms in patients with insomnia disorder. Clinicians should refer patients with insomnia for CBTi even in the presence of comorbid symptoms of depression, anxiety, and stress.