Are peer reviewers influenced by their work being cited?

Peer reviewers sometimes comment that their own journal articles should be cited by the journal article under review. Comments concerning relevant articles can be justified, but comments can also be unrelated coercive citations. Here, we used a matched observational study design to explore how citations influence the peer review process. We used a sample of more than 37,000 peer reviews from four journals that use open peer review and make all article versions available. We find that reviewers who were cited in versions after version 1 were more likely to make a favourable recommendation (odds ratio = 1.61; adjusted 99.4% CI: 1.16-2.23), whereas being cited in the first version did not improve their recommendation (odds ratio = 0.84; adjusted 99.4% CI: 0.69-1.03). For all versions of the articles, the reviewers who commented that their own articles should be cited were less likely to recommend approval compared to the reviewers who did not, with the strongest association after the first version (odds ratio = 0.15; adjusted 99.4% CI: 0.08-0.30). Reviewers who included a citation to their own articles were much more likely to approve a revised article that cited their articles compared to a revised article that did not (odds ratio = 3.5; 95% CI: 2.0-6.1). Some reviewers' recommendations depend on whether they are cited or want to be cited. Reviewer citation requests can turn peer review into a transaction rather than an objective critique of the article.