Commentary

Cognitive behavioural therapy (CBT) is the most investigated psychosocial or pharmacological intervention for adolescent depression. Early randomised clinical trials (RCTs) suggested that CBT was highly effective for depressed youths, with some of largest reported effect sizes in the adolescent mental health literature. However, recent studies have shown much smaller effects, with some reporting almost no benefit of CBT over control groups. Klein and colleagues probe this apparent drop in effectiveness by comparing the samples, settings, and methods of early and recent RCTs.

Overall, the Klein meta-analysis concludes that the more stringent methods of recent RCTs explain much of the attenuation in CBT treatment effects over the last 10 years. Unfortunately, too few studies were available to tease apart which methodological features were most critical in reducing treatment effects. Examining specific RCTs, there is reason to suspect, however, that sample characteristics may play an important role. For example, within a major CBT RCT, adolescents referred to the trial from clinical sources had worse outcomes than youths ascertained by advertisement, and this difference in referral source was associated with higher levels of hopelessness for depressed teens in clinical settings.¹ In the much publicised TADS study, adolescents whose depressions were less severe, chronic, and suicidal were more responsive to treatment, across all treatment types.² Although not assessed directly by Klein, youth and familial comorbidity also may prove to be an important predictor of CBT effectiveness. Two of the most recent studies in the Klein meta-analysis, with modest effect sizes, included youths with comorbid Conduct Disorder and adolescent offspring of depressed parents. Evidence on the robustness of CBT effects to comorbidity has been mixed.^{1, 2}

Taken together, these results suggest that CBT is likely an effective treatment with mild to moderate cases of “straightforward” adolescent depression. The effectiveness of CBT as a stand-alone treatment in severe, clinically-complicated samples is less clear, although a recent study suggests that CBT may be an effective addition to psychotropic medication for SSRI-resistant depressed adolescents.³ Additional research on the predictors and moderators of CBT effects is much-needed to inform real-world treatment planning for depressed teens and best match interventions to youths and families.