On Monday, WHO director-general Tedros Adhanom Ghebreyesus said the decision had been taken in light of a paper published last week in the Lancet.
Experts found that hydroxychloroquine – and a related medicine chloroquine – was linked to an increased risk of death and heart arrhythmias among people severely ill in hospital with coronavirus.
US President Donald Trump has been criticised after he said he had nothing to lose by taking hydroxychloroquine, which is used to treat malaria and arthritis, despite warnings it could be unsafe.
How far have the trials got?
A number of trials have been taking place across the world looking at the drug’s effectiveness in combating Covid-19.
This includes a trial – called COPCOV – to see whether the drugs could prevent Covid-19 had begun in Brighton and Oxford.
Chloroquine, hydroxychloroquine or a placebo will be given to more than 40,000 healthcare workers from Europe, Africa, Asia and South America.
What has prompted the pause?
After the Lancet study, the Medicines and Healthcare products Regulatory Agency (MHRA) asked for recruitment to the trial to be paused.
The researchers have responded to the agency addressing its concerns and remain confident the trial will resume recruiting.
Commenting on the announcement, Professor Trudie Lang, director of The Global Health Network, Nuffield Department of Medicine, University of Oxford, said: “The WHO temporarily halting the use of chloroquine in Covid-19 clinical trials highlights why we need to run carefully-designed clinical trials during outbreaks.
“This enables us to learn as quickly as possible about whether potential therapies can tackle the virus and are safe.
“Properly designed and managed clinical trials are the only way we can see whether drugs might also cause harm. They are designed to assess the safety of the drug relative to the ability to bring any benefit.
“We have long known that chloroquine can cause harmful cardiac-related side effects from the use of chloroquine in the treatment of malaria.
“Recent trials carried out in China of a lower chloroquine dose didn’t show efficacy in relation to Covid-19.
“A higher chloroquine dose could bring increased risk of harmful side effects."
She added that using chloroquine “off licence” or outside a trial does not help answer questions about its safety and can also present a risk to the patient.
Dr Stephen Griffin, associate professor in the School of Medicine, University of Leeds, said: “The WHO has taken the wise precaution of halting arms of their wide-ranging therapeutics trial relating to chloroquine (CQ) and hydroxychloroquine (HCQ).
“This is largely based upon a study published last week that retrospectively analysed thousands of patients receiving these drugs as part of their Covid-19 treatment, either alone or in combination with antibiotics.
“The study could find no evidence for a beneficial effect in patients taking these drugs.
“However, worryingly, patients appeared to be at heightened risk of cardiac complications, especially when taking CQ or HCQ alongside macrolide antibiotics.”
The University of Oxford’s RECOVERY trials, which look at potential coronavirus treatments, involve a number of medications that are licensed for use in other conditions, and includes hydroxychloroquine.
Coronavirus: Everything you need to know