Reclaiming mendelian randomization from the deluge of papers and misleading findings

Mendelian randomization (MR) is a powerful epidemiological method for causal inference. However, its recent surge in popularity has brought two concerning trends. First, the public availability of summary results from genome-wide association studies has led to an explosion of low-quality two-sample mendelian randomization (2SMR) studies. These studies add minimal - if any - value and overwhelm reviewers and journals. Second, the availability of large datasets with individual-level genotype data, like UK Biobank, has spurred the development and use of novel MR methods. However, some methods are being applied without proper testing, leading to misleading results, as exemplified by recent spurious findings that are being retracted and/or corrected relating to vitamin D. What can editors and peer reviewers do to handle the deluge of 2SMR studies and the premature application of highly complex MR methods? We advise editors to simply reject papers that only report 2SMR findings, with no additional supporting evidence. For reviewers receiving such papers, we provide a template for rejection. In addition, reviewers should demand rigorous testing of novel methods, including through the use of positive and negative controls before they are applied. Rejecting non-contributory 2SMR papers and imposing intensive scrutiny to novel methods is crucial if the scientific community is to reclaim MR.