A team of scientists at the University of Oxford have on Wednesday announced a trial to investigate the efficacy and safety of ivermectin — an antiparasitic drug — for people at more risk of serious illness from Covid-19.

Previous studies of ivermectin, which show that early administration with ivermectin can reduce viral load and the duration of symptoms in some patients with mild Covid, have generally been small or low quality.

The World Health Organisation in March and the US Food and Drug Administration (FDA) had, in April last year, recommended against the use of ivermectin in treating Covid patients. The WHO said there was a “very low certainty of evidence” on ivermectin’s effects on mortality, hospital admission and getting rid of the virus from the body.

“Safety and efficacy are important when using any drug for a new indication. @WHO recommends against the use of ivermectin for #COVID19 except within clinical trials,” Soumya Swaminathan, the global health body’s chief scientist, said in a tweet.

However, ivermectin has been taken up by doctors and by individuals self-medicating in countries, including Brazil, Bolivia, Peru and South Africa.

“Ivermectin is readily available globally, has been in wide use for many other infectious conditions so it’s a well-known medicine with a good safety profile, and because of the early promising results in some studies it is already being widely used to treat Covid-19 in several countries,” said Professor Chris Butler, from the University Oxford’s Nuffield Department of Primary Care Health Sciences, said in a statement.

“By including ivermectin in a large-scale trial, we hope to generate robust evidence to determine how effective the treatment is against Covid-19, and whether there are benefits or harms associated with its use,” he added.

The trial has so far recruited more than 5,000 volunteers from across the UK, who will be randomly assigned to receive a three-day course of ivermectin treatment. They will be followed-up for 28 days and will be compared with participants who have been assigned to receive the usual standard of National Health Service care only.

People aged 18 to 64 with certain underlying health conditions or shortness of breath from Covid-19, or aged over 65, are eligible to join the trial within the first 14 days of experiencing Covid-19 symptoms or receiving a positive test.

People with severe liver disease, who are on the blood-thinning medication warfarin, or taking other treatments known to interact with ivermectin, will be excluded.

The trial can be joined easily from anywhere in the UK either online, over the telephone or via a GP practice, and without the need for face-to-face visits with the trial team in Oxford.