Associations of prior treatment, waiting time, symptom severity, and session frequency with symptom change in CBT for depression and anxiety in primary care

BACKGROUND: Depression and anxiety are among the most prevalent mental health problems globally, with psychotherapy serving as a first-line treatment. Initial symptom severity, prior treatment history, waiting time, and session frequency may influence treatment effectiveness in routine care. METHODS: We analyzed session-by-session data from clients receiving a seven-session cognitive-behavioral therapy (CBT) program for depression (N = 2627) or anxiety (N = 3929) in primary care. Symptoms were assessed using the PHQ-9 and GAD-7 at each session. The magnitude and rate of change were examined using pre-post comparisons and linear mixed models. RESULTS: Clients showed significant reductions in both depressive (mean change -4.45 PHQ-9 points, 95% CI -4.69, -4.22) and anxiety symptoms (mean change -4.36 GAD-7 points, 95% CI -4.54, -4.17). Higher initial symptom severity was associated with faster reductions, while prior psychiatric care or previous very long-term psychotherapy were associated with smaller pre-post gains. Waiting time and session frequency were not consistently related to outcomes. CONCLUSIONS: In routine CBT, clients with higher baseline severity benefited substantially, supporting equitable access to CBT regardless of initial symptom level. Clinical improvement was driven by the total number of attended treatment sessions rather than by the rate of attendance (i.e., the number of sessions per unit of time). This supports flexible scheduling without compromising outcomes. Longer waiting times did not systematically predict poorer results, suggesting that client- versus system-driven delays may have distinct implications. Considering prior treatment history may help tailor interventions for individuals with more persistent or treatment-resistant symptom patterns.