The Dose-Response Curve in Cognitive-Behavioral Therapy for Anxiety Disorders

Anxiety disorders are among the most common mental health disorders, affecting upwards of 15 million people in the United States each year. Cognitive-behavioral therapy (CBT) is considered a first-line treatment for anxiety disorders, yet not everyone who receives this treatment actually benefits from it. To further complicate matters, therapists delivering CBT may not be able to accurately assess the progress that their patients are making in therapy. This is important because effective care depends on progress monitoring and, if progress is not being made, it is important for therapists to make recommendations for alternative treatment options so their patients stand the best chance of recovering from their anxiety.

Fortunately, the field is working towards improving the ways in which therapists assess their patients’ progress. A questionnaire called the Outcome Questionnaire-45 was developed by Lambert and colleagues to specifically assess therapy progress, and this questionnaire is widely used by therapists across the country. This questionnaire has also been used to assess the “dose-response curve” of therapy, which is the number of sessions needed for patients to make significant improvement. So far, the research shows that it takes about 8 sessions for 50% of patients receiving therapy to improve. These studies were conducted in people with a wide range of mental health problems, not just anxiety disorders, so it is unclear whether these results apply to anxiety patients specifically. Furthermore, the studies were conducted in therapy clinics that provided different types of therapy, not CBT. So we also cannot be sure whether the results apply to patients receiving CBT. 

The current study sought to address these gaps by assessing the dose-response curve using the Outcome Questionnaire-45 in a large sample of patients with anxiety disorders who received CBT. A total of 201 patients with diagnosed anxiety disorders participated in the study, and they completed the Outcome Questionnaire-45 before every treatment session. Overall, the majority of the sample (64%) showed significant improvement by the end of treatment, and it took approximately 5 sessions to make this improvement. Rates of improvement did not differ based on age, sex, race, or ethnicity, so people with different demographic characteristics stood equal chance of improving in CBT. Importantly, the dose-response curve showed that if improvement did not occur by session 10, there was only a 13% chance of showing improvement by the end of therapy. If improvement did not occur by session 15, there was only a 4% chance of showing improvement by the end of treatment.

These results tell us that the majority of patients with anxiety disorders who receive CBT benefit from this treatment, which is good news. The results also tell us that if improvement does not occur within 2-3 months of weekly therapy, the chances are very low of therapy being beneficial. The next step will be to find out why certain patients with anxiety disorders do not benefit from CBT, and how we can improve the treatment so that more people do benefit from it. This is a major area of focus in CBT research now.

Read the full paper: Levy, H. C., Worden, B. L., Davies, C. D., Stevens, K., Katz, B. W., Mammo, L., Diefenbacj, G. J., & Tolin, D. F. (in press). The dose-response curve in cognitive-behavioral therapy for anxiety disorders. Cognitive Behaviour Therapy. doi: 10.1080/16506073.2020.1771413

Pictured: Hannah Levy

Photo by: Matus Laslofi

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