Is positive placebo response in chronic schizophrenia investigator-dependent?

Retention rates in placebo- and nonplacebo-controlled clinical trials of schizophrenia

OBJECTIVE

To determine if the inclusion of a placebo control in clinical trials of schizophrenia affects retention rates in the first 35 days of inclusion relative to trials that did not have a placebo control.

METHOD

This was a retrospective study of 8 double-blind clinical trials, 5 of which had a placebo control while 3 did not. Using survival analysis, retention rates between the placebo-controlled trials (PCTs) and the nonplacebo-controlled trials (NPCTs) were compared. Screening and percentage improvement on Brief Psychiatric Rating Scale and Positive and Negative Syndrome Scale scores were compared.

RESULTS

Significantly more patients were retained in the 35-day period for NPCTs. Also, the PCT group had significantly more psychopathology at screening than did the NPCT group.

CONCLUSIONS

Differences in retention rates between PCTs and NPCTs cannot be uniquely attributed to placebo itself.