Specific Pharmacological Effects of Paroxetine Comprise Psychological but Not Somatic Symptoms of Depression

Background
Meta-analyses of placebo-controlled trials of SSRIs suggest that only a small portion of the observable change in depression may be attributed to "true" pharmacological effects. But depression is a multidimensional construct, so treatment effects may differ by symptom cluster. We tested the hypothesis that SSRIs uniquely alter psychological rather than somatic symptoms of depression and anxiety.
Method
Outpatients with moderate to severe MDD were randomly assigned to receive paroxetine (n = 120) or placebo (n = 60).
Results
Paroxetine significantly outperformed placebo on all psychological subscales of the syndrome measures, but not on any of the somatic subscales. The difference in score reduction between paroxetine and placebo was more than twice as great for the psychological symptoms compared to the somatic symptoms.
Conclusions
Paroxetine appears to have a “true” pharmacological effect on the psychological but not on the somatic symptoms of depression and anxiety. Paroxetine's influence on somatic symptoms appears to be mostly duplicated by placebo.