An Australian and Swedish investigation has found that among the hundreds of COVID-19 research papers that have been withdrawn, a retracted study linking the drug hydroxychloroquine to increased mortality was the most cited paper.

With 1,360 citations at the time of data extraction, researchers in the field were still referring to the paper "Hydroxychloroquine or chloroquine with or without a macrolide for treatment of COVID-19: a multinational registry analysis" long after it was retracted.

Authors of the analysis involving the University of Wollongong, Linköping University, and Western Sydney Local Health District wrote (pdf) that "most researchers who cite retracted research do not identify that the paper is retracted, even when submitting long after the paper has been withdrawn."

"This has serious implications for the reliability of published research and the academic literature, which need to be addressed," they said.