British medical journal the Lancet on Tuesday said it had concerns about data behind an influential article that found hydroxychloroquine increased the risk of death in Covid-19 patients, a conclusion that undercut scientific interest in the medicine championed by US President Donald Trump.

Hydroxychloroquine - which has anti-inflammatory and antiviral properties - inhibited the coronavirus in laboratory experiments but has not been proven effective in humans, particularly in placebo-controlled, randomized clinical trials considered the gold standard for data.