The Placebo Effect and Its Clinical Associations in Gambling Disorder

10 Aug 2017

Background: Gambling disorder is prevalent and functionally impairing, yet no FDA approved medications exist for its treatment. The ability of clinical trials to discriminate active treatment benefits has been hindered by the unusually high placebo response. Virtually nothing is known about baseline clinical characteristics that might be predictive of placebo response in gamblers. Methods: 152 participants assigned to placebo were pooled from multiple double-blind trials in gambling disorder. Participants were classified as placebo responders or non-responders based on a cut-off of 35% reduction in symptom severity on the Gambling Severity Scale (GSAS). Baseline group differences were characterized using t-tests and equivalent non-parametric tests as appropriate. Results: Fifty-one percent of individuals assigned to placebo treatment showed a significant clinical response to placebo. Placebo responders stayed in treatment for significantly longer, were more likely to endorse ‘enjoyment’ as a trigger for gambling, and were less likely to endorse ‘boredom’ or ‘loneliness’ as triggers for gambling. Placebo responders and non-responders did not differ significantly on age, gender, age at symptom onset, baseline symptom severity, comorbidities, or likelihood of having received a previous treatment. Conclusions: Predictors of placebo response for gambling disorder appear markedly different from those reported for other mental health disorders.