Good morning or good evening: Daytime and cortisol as modulators of exposure therapy outcomes.

BACKGROUND: Although exposure therapy is considered the gold standard treatment for anxiety disorders, many patients do not respond sufficiently to it. This study investigated the effects of the time of day at which exposure therapy is delivered and endogenous cortisol levels during exposure on treatment success in patients with fear of spiders. It was hypothesized that individuals undergoing exposure therapy in the morning would experience greater symptom reductions compared to those undergoing therapy in the evening, and that higher endogenous cortisol levels would predict greater symptom reductions. METHOD: 53 participants with symptoms of spider phobia were recruited to complete a four-hour group-based exposure therapy starting either at 8 a.m. or 5 p.m. in a double-blind design. Symptoms of spider phobia were assessed using the Structured Clinical Interview for DSM-IV. Therapy outcomes were assessed before, one week after therapy and at 3-months' follow-up, using the Spider Phobia Questionnaire (SPQ), the Fear of Spiders Questionnaire (FSQ), and a behavioral approach test (BAT). RESULTS: Both phobic fear (FSQ: η²ₚ=0.70; SPQ: η²ₚ=0.59) and avoidance behavior (η²ₚ=0.70) significantly improved following exposure therapy. The morning group showed higher cortisol levels than the evening group (p = 0.036), however, symptom improvement did not differ between the groups (all p > 0.05). Exploratory analyses revealed that a lower cortisol change (AUCi) during individual exposure was associated with greater improvements in phobic fear (FSQ: η²ₚ=0.20; SPQ: η²ₚ=0.11). CONCLUSION: Although daytime was not found to modify exposure therapy treatment success, preliminary evidence points to a potential role of cortisol change, warranting further investigation.