In a multi-center study conducted in Great Britain and Australia, 86 adults with mental retardation (IQ < 75) and aggressive behavior were randomized to double-blind treatment with Risperdal (mean dose, 1.8 mg/day), Haldol (mean dose, 2.9 mg/day), or placebo. The primary outcome was score on the modified overt aggression scale (MOAS) at 4 weeks. The results were that placebo reduced the MOAS score by more than either of the active treatments, with the difference close to being statistically significant (p=.07 vs. Risperdal and p=.06 vs. Haldol) (Tyrer P, et al., Lancet 2008;371(9606):57-63).
TCPR’s Take: These results are differ- ent from some prior studies which showed a benefit of Risperdal in this population. One likely reason is that past studies included a “placebo run-in” phase, in which patients who responded rapidly to placebo were excluded from the double-blind study. This had the effect of minimizing the placebo effect in the main study and increasing the likelihood of a drug vs. placebo difference. These investigators did not include the placebo run-in in order to make the design more similar to clinical practice. These results imply that in aggressive mentally retarded adults, placebo effects are extremely powerful, and perhaps prescribing a multivitamin (with great fanfare and high expectations) is as effective as prescribing an antipsychotic, with far fewer side effects.
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