This is a well-designed study which has many strengths, including its large sample size, long duration of follow-up with low drop-out rates, and using valid symptom scales to assess outcomes.
As the researchers say, previous research has led to CBT becoming an established treatment for depression.
But this large-scale randomised controlled trial arguably provides the strongest evidence to date about the effectiveness of adding CBT to antidepressant medication for people whose symptoms have not responded to six months of medication.
However, the study does contain some minor limitations. For example, participants and researchers were aware of treatment allocation – an unvoidable constraint with this type of study – you can’t give people ‘placebo’ CBT.
This study nevertheless provides further evidence on the effectiveness of CBT to treat depression, particularly in those who have not responded to antidepressants alone.