Impact of active placebo controls on estimated drug effects in randomised trials: a systematic review of trials with both active placebo and standard placebo.

Background: An estimated 60% of pharmacological randomised trials use placebo control interventions to blind (i.e. mask) participants.

Adherence to the PRISMA-P 2015 reporting guideline was inadequate in systematic review protocols.

Objectives: The objective of the study was to investigate to which degree systematic review protocols adhere to the Preferred Reporting Items for Systematic review and Meta-Analysis Protocols (PRISMA-P) reporting guideline.

Study Design And Setting: We randomly sampled 50 publications of systematic review protocols indexed in PubMed and 50 protocols uploaded to the International Prospective Register of Systematic Reviews (PROSPERO) from 2016 onward. Two authors independently extracted data and assessed adherence to the 26 items specified by PRISMA-P.