The BMJ has locked horns with Facebook and the gatekeepers of international fact checking after one of its investigations was wrongly labelled with “missing context” and censored on the world’s largest social network. Rebecca Coombes and Madlen Davies report On 3 November Howard Kaplan, a retired dentist from Israel, posted a link to a BMJ investigation article in a private Facebook group.1 The investigation reported poor clinical trial research practices occurring at Ventavia, a contract research company helping to carry out the main Pfizer covid-19 vaccine trial.2 The article brought in record traffic to bmj.com and was widely shared on Twitter, helping it achieve the second highest “Altmetric” score of all time across all biomedical publications.3 But a week after his posting Kaplan woke up to a message from Facebook (fig 1). Fig 1 Clockwise from top left: Facebook’s “missing context” notice; administrators of a private group were warned of a “partly false” post; Facebook’s warning on Howard Kaplan’s original post; Cochrane’s tweet after being “shadowbanned” by Instagram “The Facebook Thought Police has issued me a dire warning,” he wrote in a new post. “Facebook’s ‘independent fact-checker’ doesn’t like the wording of the article by the BMJ. And if I don’t delete my post, they are threatening to make my posts less visible. Obviously, I will not delete my post . . . If it seems like I’ve disappeared for a while, you’ll know why.”4 Kaplan was not the only Facebook user having problems. Soon, several BMJ readers were alerting the journal to Facebook’s censorship. Over the past two months the journal’s editorial staff have been navigating the opaque appeals process without success, and still today their investigation remains obscured on Facebook. The experience has highlighted serious concerns about the “fact checking” being undertaken by third party …