A paper on a clinical trial of metformin for the treatment of COVID-19 has been retracted nearly two years after the authors flagged data issues that resulted in an expression of concern.
The results of the Brazil-based TOGETHER trial, published in December 2021 in The Lancet Regional Health–Americas, found metformin was no better than placebo at improving health outcomes in people with COVID-19. The authors of the now-retracted study requested a correction to the article in 2023 after realizing they had included an incorrect number of primary outcome events when reporting the result.
The journal issued an expression of concern in February 2024, citing “errors in the total population considered for the analysis.” The journal retracted the article on October 21, 2025. The “unintentional” error by the authors “led to an inappropriate decision to stop the trial,” meaning the reliability of the findings was “compromised,” according to the retraction notice.
