Objective: We investigated the predictive validity of the cortisol awakening response (CAR) in patients with non-seasonal major depression.

Method: Patients were treated with sertraline in combination with bright or dim light therapy for a 5-week period. Saliva cortisol levels were measured in 63 patients, as an awakening profile, before medication and light therapy started. The CAR was calculated by using three time-points: awakening and 20 and 60 min after awakening.

Results: Patients with low CAR had a very substantial effect of bright light therapy compared with dim light therapy, whereas patients with a high CAR had no effect of bright light therapy compared with dim light therapy.

Conclusion: High CAR was associated with an impairment of the effect of bright light therapy. This result raises the question of whether bright light acts through a mechanism different from that of antidepressants.