An Oxford University-led trial investigating hydroxychloroquine as a preventative treatment against COVID-19 may never find out if it is effective, BBC News reported on Thursday.
While ineffective in hospitalised patients, investigators hope the drug might work if given earlier on.
The trial is aiming to enrol 40,000 frontline workers around the world.
Nick White, one of the study's investigators, said that "I don't think there's been a more politicised and controversial medicine than hydroxychloroquine."
The Medicines and Healthcare products Regulatory Agency halted hydroxychloroquine trials, following a now-discredited paper in The Lancet claiming it caused harms, and trials resumed in late June.
However, the investigators suggested that these concerns over safety have made it difficult to get participants.
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