Objective: To determine whether cognitive behavior therapy (CBT) for bulimia nervosa has a specific therapeutic effect and determine whether a simplified behavioral treatment (BT) of CBT is as effective as the full treatment.
Design: Randomized controlled trial involving three psychological treatments. Two planned comparisons, CBT with interpersonal psychotherapy (IPT), and CBT with BT. Closed 12-month follow-up period. Independent assessors.
Setting: Secondary referral center.
Patients: Seventy-five consecutively referred patients with bulimia nervosa. Patients with concurrent anorexia nervosa were excluded.
Interventions: Cognitive behavior therapy, IPT, BT conducted on an individual outpatient basis. There were nineteen sessions over 18 weeks. Six experienced therapists administered all three treatments. There was no concurrent treatment.
Main outcome measure: Frequency of binge eating and purging.
Results: High rate (48%) of attrition and withdrawal among the patients who received BT. Over follow-up, few patients undergoing BT met criteria for a good outcome (cessation of all forms of binge eating and purging). Patients in the CBT and IPT treatments made equivalent, substantial, and lasting changes across all areas of symptoms, although there were clear temporal differences in the pattern of response, with IPT taking longer to achieve its effects.
Conclusions: Bulimia nervosa may be treated successfully without focusing directly on the patient's eating habits and attitudes to shape and weight. Cognitive behavior therapy and IPT achieved equivalent effects through the operation of apparently different mediating mechanisms. A further comparison of CBT and IPT is warranted. The behavioral version of CBT was markedly less effective than the full treatment.