The placebo effect and its clinical associations in gambling disorder.

BACKGROUND: Although gambling disorder is prevalent and functionally impairing, no FDA-approved medications exist for its treatment. The ability of clinical trials to detect the benefits of active treatment has been hindered by an unusually high placebo response. Virtually nothing is known about baseline clinical characteristics that might predict placebo response in those with gambling disorder.

METHODS: Participants (N = 152) assigned to placebo were pooled from multiple double-blind trials of 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 Symptom Assessment Scale. Baseline group differences were characterized using t tests and equivalent non-parametric tests as appropriate.

RESULTS: Fifty-one percent of individuals assigned to placebo showed a significant clinical response. Compared with non-responders, placebo responders remained in treatment for significantly longer, were more likely to report "enjoyment" as a trigger for gambling, and were less likely to state that "boredom" or "loneliness" triggered their gambling. Placebo responders and non-responders did not differ significantly in age, sex, 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 illnesses.