The effects of cognitive and behavioural therapies for anxiety disorders on depression: a meta-analysis.

Background: The effects of cognitive behavioural therapy of anxiety disorders on depression has been examined in previous meta-analyses, suggesting that these treatments have considerable effects on depression. In the current meta-analysis we examined whether the effects of treatments of anxiety disorders on depression differ across generalized anxiety disorder (GAD), social anxiety disorder (SAD) and panic disorder (PD). We also compared the effects of these treatments with the effects of cognitive and behavioural therapies of major depression (MDD).
Method: We searched PubMed, PsycINFO, EMBASE and the Cochrane database, and included 47 trials on anxiety disorders and 34 trials on MDD.
Results: Baseline depression severity was somewhat lower in anxiety disorders than in MDD, but still mild to moderate in most studies. Baseline severity differed across the three anxiety disorders. The effect sizes found for treatment of the anxiety disorders ranged from g = 0.47 for PD, g = 0.68 for GAD and g = 0.69 for SAD. Differences between these effect sizes and those found in the treatment of MDD (g = 0.81) were not significant in most analyses and we found few indications that the effects differed across anxiety disorders. We did find that within-group effect sizes resulted in significantly (p < 0.001) larger effect sizes for depression (g = 1.50) than anxiety disorders (g = 0.73-0.91). Risk of bias was considerable in the majority of studies.
Conclusions: Patients participating in trials of cognitive behavioural therapy for anxiety disorders have high levels of depression. These treatments have considerable effects on depression, and these effects are comparable to those of treatment of primary MDD.