Exploratory Review of Placebo Characteristics Reported in Randomised Placebo Controlled Antidepressant Drug Trials

Abstract

Introduction:

Systematic reviews of randomised placebo controlled trials of antidepressants have found small and decreasing differences in outcome between pharmacological and placebo arms. Increased knowledge of placebo characteristics may provide greater understanding of antidepressant pharmacological effect. We conducted a systematic review to identify the presence of key placebo characteristics in a sample of antidepressant clinical trials.

Methods:

82 randomised placebo controlled trials of antidepressants, selected in 2 previous systematic reviews (Walsh et al. 2002; NICE 2009), were examined. Presence of placebo characteristics documented using detailed standardised form, with 5 domains: health care environment, practitioner characteristics, patient characteristics, practitioner-patient interaction, and non-pharmaceutical drug characteristics. First authors contacted where possible, and further clarification sought on placebo characteristics within trials.

Results:

Percentage of trials reporting placebo characteristics within the 5 domains: health care setting 100%, environment 5%; practitioner profession 18%, status 0%, incentives 0%, gender 10%, age 4%, beliefs 6%; patient age 85%, gender 91%, ethnicity 41%, diagnosis and severity 100%, recruitment 16%, incentives 12%, co-morbidity 12%, expectation 0%, beliefs 0%; patient-practitioner interaction type of care 10%, number of visits 94%, empathy and congruence 2%; drug form 45% and frequency 57%.

Discussion:

Placebo characteristics represent confounding variables which, if not adequately controlled for, could distort findings and conclusions about efficacy. The lack of systematic recording of many placebo characteristics in antidepressant drug trials is a cause for concern. To reduce imprecision and increase generalisability, future antidepressant clinical trials should consider the impact of key placebo characteristics and record their presence when disseminating findings.

Key words

depression - placebo - antidepressants - review

• References

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