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Certainty of genuine treatment increases drug responses among intellectually disabled patients
Karin B Jensen1, Irving Kirsch2, Moa Pontén2
1From the Department of Clinical Neuroscience (K.B.J., M.P., A.R.), Karolinska Institute, Sweden; Program in Placebo Studies (I.K., T.J.K.), BIDMC, Harvard Medical School; Department of Psychiatry (K.Y., R.L.G.), Massachusetts General Hospital, Boston; Institut des Sciences Cognitives (V.d.P., A.C.), Bron; Université Claude Bernard Lyon 1 (V.d.P., A.C.); Centre de Référence Déficiences Intellectuelles de Causes Rares (V.d.P., A.C.), Hôpital Femmes Mères Enfants, Hospices Civils de Lyon; and EPICIME-CIC1407/INSERM (A.C.), Bron, France. Karin.Jensen@ki.se.
Objective:
To determine the placebo component of treatment responses in patients with intellectual disability (ID).
Methods:
A statistical meta-analysis comparing bias-corrected effect sizes (Hedges g) of drug responses in open-label vs placebo-controlled clinical trials was performed, as these trial types represent different certainty of receiving genuine treatment (100% vs 50%). Studies in fragile X, Down, Prader-Willi, and Williams syndrome published before June 2015 were considered.
Results:
Seventeen open-label trials (n = 261, 65% male; mean age 23.6 years; mean trial duration 38 weeks) and 22 placebo-controlled trials (n = 721, 62% male; mean age 17.1 years; mean trial duration 35 weeks) were included. The overall effect size from pre to post treatment in open-label studies was g = 0.602 (p = 0.001). The effect of trial type was statistically significant (p = 0.001), and revealed higher effect sizes in studies with 100% likelihood of getting active drug, compared to both the drug and placebo arm of placebo-controlled trials. We thus provide evidence for genuine placebo effects, not explainable by natural history or regression toward the mean, among patients with ID.
Conclusions:
Our data suggest that clinical trials in patients with severe cognitive deficits are influenced by the certainty of receiving genuine medication, and open-label design should thus not be used to evaluate the effect of pharmacologic treatments in ID, as the results will be biased by an enhanced placebo component.