The effects of six-day SSRI administration on diurnal cortisol secretion in healthy volunteers

RATIONALE: Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis has been widely reported in depression, and evidence suggests that selective serotonin reuptake inhibitors (SSRIs) might exert their therapeutic effects through altering cortisol secretion. OBJECTIVE: This study assessed the effects of SSRI administration on diurnal cortisol secretion in healthy volunteers. METHODS: Sixty-four healthy men and women were randomised to receive either 10 mg escitalopram or placebo for six days in a double-blind fashion. On day six of medication, saliva samples were obtained at home for measurement of diurnal cortisol parameters (cortisol slope, cortisol awakening response, total daily cortisol output). RESULTS: Women receiving escitalopram had significantly steeper cortisol slopes across the day compared with those receiving placebo (F(1, 36) = 7.54, p = 0.009). This alteration in cortisol slope was driven by increases in waking cortisol levels (F(1, 35) = 9.21, p = 0.005). Escitalopram did not have any significant effect on the cortisol awakening response or the total daily cortisol output. CONCLUSIONS: Flattened cortisol slopes have been seen in depression. The results of this study suggest that escitalopram might exert its therapeutic effect in women in part through correction of a flattened diurnal cortisol rhythm.