Longitudinal effects of the SSRI paroxetine on salivary cortisol in Major Depressive Disorder

Hypothalamic-pituitary-adrenal (HPA)-axis dysregulation is a prominent finding in more severe Major Depressive Disorder (MDD), and is characterized by increased baseline cortisol levels at awakening (BCL), blunted cortisol awakening response (CAR) and increased area under the cortisol curve (AUC). Selective serotonin reuptake inhibitors (SSRIs) appear to normalize HPA-axis dysfunction, but this is hardly investigated longitudinally. We studied salivary BCL, CAR and AUC at awakening and 30min thereafter. We compared measurements in initially drug-free MDD-patients with healthy controls (HCs) at study-entry. In patients, we repeated measures after 6 and 12 weeks' treatment with the SSRI paroxetine. Non-responding patients received a randomized dose-escalation after six weeks' treatment. We found no significant study-entry differences in BLC, CAR or AUC between MDD-patients (n=70) and controls (n=51). In MDD-patients, we found general decreases of BCL and AUC during paroxetine treatment (p≤0.007), especially in late and non-responders. Importantly, while overall CAR did not change significantly over time, it robustly increased over 12 weeks especially when patients achieved remission (p≤0.041). The dose-escalation intervention did not significantly influence CAR or other cortisol parameters. In conclusion, paroxetine seems to interfere with HPA-axis dysregulation, reflected in significant overall decreases in BCL and AUC during treatment. Paroxetine appears to decrease HPA-axis set-point in MDD, which might result in increased HPA-axis activity over time, which is further improved when patients achieve remission (ISRCTN register nr. ISRCTN44111488).