OBJECTIVES: To assess whether and how investigators of placebo controlled randomised trials inform participants of their treatment allocation at trial closure and to assess barriers to feedback. DESIGN: Postal survey with a semistructured questionnaire. PARTICIPANTS: All investigators who published a placebo controlled randomised trial in 2000 in five leading medical journals, and a random sample of 120 trials listed in the national research register database. MAIN OUTCOME MEASURES: Number of investigators who informed participants of their treatment allocation at trial closure, methods for delivering the information, and barriers to unmasking treatment. RESULTS: 45% of investigators informed either all or most participants of their treatment allocation, and 55% did not inform any participant or only informed those who asked. The main reasons for not informing participants were that the investigators never considered this option (40%) or to avoid biasing results at study follow up (24%). CONCLUSION: Further research is required to examine sensitive ways to communicate treatment information to trial participants
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