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Re: SSRIs vs Placebo.... PLEASE READ Dan Perkins

Posted by ed_uk on January 4, 2005, at 15:45:08

In reply to Re: SSRIs vs Placebo.... PLEASE READ, posted by Dan Perkins on January 4, 2005, at 14:41:22

>On this placebo topic, I read once that in clinical trials the drug companies supply the placebo pills as well as the active (the real thing) pills and that they sometimes ad substances to the placebo pill that mimic some of the negative effects of the active pills so that the side-effects reported in the active group are relatively comparable to those reported in the placebo group (thus allowing the drug company to downplay the side-effects of their new pill).

Hi Dan,

A 'placebo' pill which contains a pharmacologically active drug is called an 'active placebo'. A active placebo is designed to mimic the side effects of the test drug eg. atopine might be used as an active placebo to mimic the side effects of a TCA because atropine, like the TCAs, causes anticholinergic side effects.

The aim of using an active placebo is to make it more difficult for the participants and assessors to tell who is taking the active drug and who is taking a placebo. This is supposed to reduce bias.

Have a look at this....

Active placebos versus antidepressants for depression.

Moncrieff J, Wessely S, Hardy R.

Psychiatry, University College London, Warley hospital, Mascalls Lane, Brentwood, Essex, UK, CM14 4TU.

BACKGROUND: Although there is a consensus that antidepressants are effective in depression, placebo effects are also thought to be substantial. Side effects of antidepressants may reveal the identity of medication to participants or investigators and thus may bias the results of conventional trials using inert placebos. Using an 'active' placebo which mimics some of the side effects of antidepressants may help to counteract this potential bias. OBJECTIVES: To investigate the efficacy of antidepressants when compared with 'active' placebos. SEARCH STRATEGY: The Cochrane Collaboration Depression, Anxiety and Neurosis review groups's search strategy was used to search MEDLINE (1966-2000), PsychLIT (1980-2000) and EMBASE (1974-2000) and this was last done in July 2000. Reference lists from relevant articles and textbooks were searched and 12 specialist journals were handsearched up to 1996. SELECTION CRITERIA: Randomised and quasi randomised controlled trials comparing antidepressants with active placebos in people with depression. DATA COLLECTION AND ANALYSIS: Since many different outcome measures were used a standard measure of effect was calculated for each trial. A subgroup analysis of inpatient and outpatient trials was conducted. Two reviewers independently assessed whether each trial met inclusion criteria. MAIN RESULTS: Nine studies involving 751 participants were included. Two of them produced effect sizes which showed a consistent and statistically significant difference in favour of the active drug. Combining all studies produced a pooled estimate of effect of 0.39 standard deviations (confidence interval, 0.24 to 0.54) in favour of the antidepressant measured by improvement in mood. There was high heterogeneity due to one strongly positive trial. Sensitivity analysis omitting this trial reduced the pooled effect to 0.17 (0.00 to 0.34). The pooled effect for inpatient and outpatient trials was highly sensitive to decisions about which combination of data was included but inpatient trials produced the lowest effects. REVIEWER'S CONCLUSIONS: The more conservative estimates from the present analysis found that differences between antidepressants and active placebos were small. This suggests that unblinding effects may inflate the efficacy of antidepressants in trials using inert placebos. Further research into unblinding is warranted.





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