Hydroxychloroquine champion Didier Raoult — 46 retractions, 218 concerns

Didier Raoult was one of France's most prominent microbiologists, director of the IHU Méditerranée Infection institute in Marseille, and a specialist in infectious diseases. He built his reputation over decades studying emerging pathogens and was known for his aggressive, confident style. He was a media figure whose pronouncements carried enormous weight in France, particularly during the COVID-19 pandemic.

On March 17, 2020, Raoult announced results from a 24-patient trial claiming hydroxychloroquine, combined with azithromycin, was effective against COVID-19. The study was published in the International Journal of Antimicrobial Agents but was later described by the publisher as not meeting the society's expected standard. Despite the weak evidence, the study was cited by politicians including Donald Trump and Jair Bolsonaro, and hydroxychloroquine became a political flashpoint worldwide. The study was retracted in December 2024 for lack of informed consent and methodological problems.

The fallout was enormous. As of 2025, 46 of Raoult's publications had been retracted and at least 218 had received expressions of concern — the largest number of flagged papers for any single researcher. In December 2022, PLOS flagged 48 articles. In April 2024, more than 100 expressions of concern were issued in a single action. Raoult was also found to have conducted illegal clinical trials on a tuberculosis treatment since 2017 without regulatory approval, targeting vulnerable patients. The French drug safety agency imposed severe sanctions on his institute. Raoult retired in summer 2022.