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Association between conflicts of interest and favourable recommendations in clinical guidelines, advisory committee reports, opinion pieces, and narrative reviews: systematic review

BMJ 2020; 371 doi: (Published 09 December 2020) Cite this as: BMJ 2020;371:m4234
  1. Camilla H Nejstgaard, doctoral student1 2 3 4,
  2. Lisa Bero, professor5,
  3. Asbjørn Hróbjartsson, professor1 2 3,
  4. Anders W Jørgensen, ENT specialist6,
  5. Karsten J Jørgensen, acting director4,
  6. Mary Le, general practitioner7,
  7. Andreas Lundh, senior researcher1 2 3 8
  1. 1Centre for Evidence-Based Medicine Odense (CEBMO), Odense University Hospital, Odense, Denmark
  2. 2Department of Clinical Research, University of Southern Denmark, Odense, Denmark
  3. 3Open Patient data Exploratory Network (OPEN), Odense University Hospital, Odense, Denmark
  4. 4Nordic Cochrane Centre, Rigshospitalet, Copenhagen, Denmark
  5. 5Center for Bioethics and Humanities, University of Colorado, CO, USA
  6. 6ENT Clinic Hobro, Hobro, Denmark
  7. 7Stasjonsgata Legekontor, Hokksund, Norway
  8. 8Department of Infectious Diseases, Hvidovre Hospital, Hvidovre, Denmark
  1. Correspondence to: C H Nejstgaard Camilla.hansen3{at}
  • Accepted 10 October 2020


Objective To investigate the association between conflicts of interest and favourable recommendations in clinical guidelines, advisory committee reports, opinion pieces, and narrative reviews.

Design Systematic review.

Eligibility criteria Studies that compared the association between conflicts of interest and favourable recommendations of drugs or devices (eg, recommending a drug) in clinical guidelines, advisory committee reports, opinion pieces (eg, editorials), or narrative reviews.

Data sources PubMed, Embase, Cochrane Methodology Register (from inception to February 2020), reference lists, Web of Science, and grey literature.

Data extraction and analysis Two authors independently extracted data and assessed the methodological quality of the studies. Pooled relative risks and 95% confidence intervals were estimated using random effects models (relative risk >1 indicates that documents with conflicts of interest more often had favourable recommendations than documents with no conflicts of interest). Financial and non-financial conflicts of interest were analysed separately, and the four types of documents were analysed separately (preplanned) and combined (post hoc).

Results 21 studies that analysed 106 clinical guidelines, 1809 advisory committee reports, 340 opinion pieces, and 497 narrative reviews were included. Unpublished data were received for 11 studies (eight full datasets and three summary datasets). 15 studies showed risk of confounding because the compared documents could differ in factors other than conflicts of interest (eg, different drugs used for different populations). The relative risk for associations between financial conflicts of interest and favourable recommendations for clinical guidelines was 1.26 (95% confidence interval 0.93 to 1.69; four studies of 86 clinical guidelines), for advisory committee reports was 1.20 (0.99 to 1.45; four studies of 629 advisory committee reports), for opinion pieces was 2.62 (0.91 to 7.55; four studies of 284 opinion pieces), and for narrative reviews was 1.20 (0.97 to 1.49; four studies of 457 narrative reviews). An analysis of all four types of documents combined supported these findings (1.26, 1.09 to 1.44). In one study that investigated specialty interests, the association between including radiologists as authors of guidelines and recommending routine breast cancer was: relative risk 2.10, 95% confidence interval 0.92 to 4.77; 12 clinical guidelines).

Conclusions We interpret our findings to indicate that financial conflicts of interest are associated with favourable recommendations of drugs and devices in clinical guidelines, advisory committee reports, opinion pieces, and narrative reviews. Limitations of this review were risk of confounding in the included studies and the statistical imprecision of individual analyses of each document type. It is not certain whether non-financial conflicts of interest influence recommendations.

Systematic review registration Cochrane Methodology Review Protocol MR000040.


  • Contributors: AL conceived the study. CHN, AH, and AL primarily developed the protocol, with contributions from LB, KJJ, and AWJ. The protocol was based on a previous protocol developed by AL, AWJ, and LB.51 CHN and either AWJ or AL assessed studies for inclusion. CHN and either ML, AWJ, or AL extracted data and assessed studies for methodological quality. CHN analysed the data. All authors interpreted the data. CHN wrote the draft review of the manuscript and all authors revised the manuscript. CHN is guarantor. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted.

  • Funding: No specific funding.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at and declare no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; and no other relationships or activities that could appear to have influenced the submitted work. LB is coauthor of one of the included studies. LB was not involved in the study inclusion, data extraction, and methodological quality assessment of any studies.

  • The lead author (CHN) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned have been explained.

  • Dissemination to participants and related patient and public communities: No specific plan beyond dissemination through journal publication and news media.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

Data availability statement

No additional data available.

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