Drugs normally used to treat malaria, hydroxychloroquine and chloroquine, have been touted as potential treatments for coronavirus.

The treatments have been promoted and used by some world leaders, but concerns have been raised about their safety and efficacy.

We've looked at what we know so far about these drugs.

Why have these drugs gained prominence?

US President Donald Trump revealed in May that he was taking hydroxychloroquine as a preventative measure against Covid-19, but later said he'd stopped.

Mr Trump has repeatedly referred to its potential. At a press conference in April, he said: "What do you have to lose? Take it."

Following Mr Trump's comments, there was a sharp increase reported in prescriptions in the US for both hydroxychloroquine and the related drug, chloroquine.

Brazilian President Jair Bolsonaro claimed in a video that "hydroxychloroquine is working in all places." This was removed by Facebook for breaching its misinformation guidelines.

There's also been a global surge in demand for them.

What are the concerns about safety?

There is concern in the scientific community about using such drugs to treat coronavirus.

Hydroxychloroquine is safe for treating malaria, and conditions like lupus or arthritis, but so far no clinical trials have recommended it for use against Covid-19.

Image copyright Reuters

President Trump took the malaria drug hydroxychloroquine as a preventative measure against Covid-19

Safety fears were highlighted following research published in the Lancet medical journal that reviewed the medical records of thousands of coronavirus patients.

This suggested there were no benefits to taking the drugs - and they could even increase the risk of heart problems.

But the Lancet has now put out "an expression of concern" about the research after questions about the data that was used by a group of scientists.

The World Health Organization (WHO), which had halted some trials using hydroxychloroquine because of these safety concerns, announced on 3 June that it would resume them.

Is there evidence they work against Covid-19?

There are trials in various countries on using the drugs to prevent the illness, sometimes involving frontline workers taking it as a prophylactic.

A trial is underway across Europe, Africa, Asia and South America, testing 40,000 people with either hydroxychloroquine, chloroquine or a placebo to see if it's effective in preventing the virus.

Other studies are looking into whether it can help patients who already have Covid-19.

In the US, various trials are taking place for a combination of drugs including chloroquine, hydroxychloroquine and an antibiotic called azithromycin, for treating Covid-19 patients.

Nigeria has said it will continue with its own planned clinical trials.

The country's drugs approval agency said it does not dispute the WHO's safety warnings, but wanted to generate data from tests on the local population.

Morocco, Algeria and Senegal have also decided to continue trials, although Kenya says it will be suspending its planned studies.

At the moment, there's not a great deal of evidence to show whether or not they're effective for either prevention or treatment.

Results that have come out from one clinical trial of hydroxychloroquine by the University of Minnesota in the US show it is not effective at preventing Covid-19.

Over 800 US and Canadian health care workers and other individuals exposed to the virus were given either a placebo or the drug. No significant difference was found in the percentages of each group who got Covid-19.

Are any countries already using these drugs?

In late March, the US Food and Drugs Administration (FDA) granted "emergency use" authorisation for these drugs in the treatment of Covid-19 for a limited number of hospitalised cases.

That means that in specific circumstances only, hospitals can request and use the medicines for Covid-19 treatment.

But on 24 April, the FDA issued a warning about the dangers of using the substances because of reports of heart rhythm problems in patients.

Image copyright Reuters

 American scientists have begun a trial to see if chloroquine will help treat coronavirus

Other countries also deploying these drugs in various settings.

Brazil has relaxed its restrictions to allow doctors to prescribe them to patients with mild coronavirus symptoms, not just those in a serious condition in hospital.

And the US government has sent two million doses to Brazil for frontline workers and those receiving treatment in hospitals.

The Indian government has expanded the use of the drug as a preventative medicine - but only under medical supervision - for healthcare workers in non-coronavirus environments, and police working in areas with high rates of Covid-19.

France, which had authorised hospitals to prescribe them for patients with Covid-19, later reversed the decision after the country's medical watchdog warned of side effects.