Background Medical research so flawed as to be retracted may put patients at risk by influencing treatments.

Objective To explore hypotheses that more patients are put at risk if a retracted paper appears in a journal with a high impact factor (IF) so that the paper is widely read; is written by a ‘repeat offender’ author who has produced other retracted research; or is a clinical trial.

Methods English language papers (n=788) retracted from the PubMed database between 2000 and 2010 were evaluated. Only those papers retracting research with humans or freshly derived human material were included; 180 retracted primary papers (22.8%) met inclusion criteria. Subjects enrolled and patients treated were tallied, both in the retracted primary studies and in 851 secondary studies that cited a retracted primary paper.

Results Retracted papers published in high-IF journals were cited more often (p=0.0004) than those in low-IF journals, but there was no difference between high- and low-IF papers in subjects enrolled or patients treated. Retracted papers published by ‘repeat offender’ authors did not enrol more subjects or treat more patients than papers by one-time offenders, nor was there a difference in number of citations. However, retracted clinical trials treated more patients (p=0.0002) and inspired secondary studies that put more patients at risk (p=0.0019) than did other kinds of medical research.

Conclusions If the goal is to minimise risk to patients, the appropriate focus is on clinical trials. Clinical trials form the foundation of evidence-based medicine; hence, the integrity of clinical trials must be protected.