A doctor has warned that patients with auto-immune diseases will be negatively impacted by a global stockpiling of hydroxychloroquine, after US President Donald Trump said he is taking it as a preventative measure against Covid-19.

Consultant rheumatologist Dr Laura Durcan said there is "absolutely no data" that hydroxychloroquine is effective for use against the new coronavirus.

Speaking on RTÉ's Today with Sarah McInerney, Dr Durcan said taking the anti-malarial drug for use to prevent Covid-19 is "absolute lunacy".

Studies have found it to be ineffective and the US Food and Drug Administration has warned of the potential for serious side effects associated with it.

The drug is used to treat chronic auto-immune disorders such as lupus, rheumatoid arthritis and malaria.

There is no medical evidence to suggest anti-malarial drugs offer protection against Covid-19.

Dr Duncan said she is worried that people will ignore the advice of health authorities and follow Mr Trump's lead, which could result in patients with life-threatening auto immune disease, and who need the drug, not being able to access it.

She said it is derived from a type of tree bark and has been studied for anti-viral properties, but not shown to be effective for viral infections, including Covid-19.

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Dr Rosemary Leonard, a GP in south London, said the drug can cause kidney and liver damage and an irregular heart beat.

She said it can also cause hair loss and said it is "extraordinary" that Mr Trump "is peddling it like a drug pusher when it causes more harm than good".

Speaking on the same programme, she said the best thing anyone could do to reduce their risks of health problems from Covid-19 is to lose weight if they are overweight.

Dr Leonard said we will have to wait and see how vaccine trials are going and continue to wash our hands and socially distance.

Mr Trump, noting that he has tested negative for the virus and shows no symptoms, said he had been taking the drug as a preventative measure for about a week-and-a-half.

"I take a pill every day," he said, adding that he combines this with zinc.

Asked why, he said: "Because I think it's good. I've heard a lot of good stories."

US House Speaker Nancy Pelosi said it's "not a good idea" for Mr Trump to be taking the drug as a potential treatment for the coronavirus.

She told CNN: "He's our president, and I would rather he not be taking something that has not been approved by the scientists, especially in his age group and his, shall we say, weight group ... morbidly obese, they say."

Senate Minority Leader Chuck Schumer called Mr Trump's decision to take the drug "reckless".

"It gives people false hope, has people avoid real medical attention, and can actually cause them trouble. It is just dangerous what he did," Mr Schumer said on MSNBC.

Mr Trump said his use of the medicine was approved by the White House physician, Sean Conley. However, Mr Trump insisted that he, not the doctor, took the first step.

"I asked him, 'what do you think?' He said, 'if you'd like it.' I said 'yeah, I'd like it'."

Dr Conley later issued a statement saying that he had agreed to Mr Trump using the anti-viral drug "after numerous discussions" between them about the pros and cons.

"We concluded the potential benefit from treatment outweighed the relative risk," Dr Conley said.

The US Food and Drug Administration warns against giving hydroxychloroquine for either prevention or treatment of the coronavirus, noting reported side effects including "serious heart rhythm problems in patients with Covid-19". Only emergency use is authorised under temporary rules.

Earlier this month, a medical paper out of New York suggested that combining hydroxychloroquine with the dietary supplement zinc sulfate, which has antiviral properties, could create a more effective treatment against coronavirus.

But Matthew Heinz, an Arizona doctor who served under Barack Obama's government, said medicines like hydroxychloroquine are not "benign" and open for unregulated use.

"I cannot stress enough how reckless it is to encourage anybody to take hydroxychloroquine or any other unproven remedy," he said in a statement.

Biotech company Moderna's experimental Covid-19 vaccine, the first to be tested in the US, produced protective antibodies in a small group of healthy volunteers, according to very early data released yesterday.

The data comes from eight people who took part in a 45-subject safety trial that kicked off in March.

The Moderna vaccine is one of more than 100 under development intended to protect against the new coronavirus.

Overall, the study showed the vaccine was safe and all study participants produced antibodies against the virus.

The only drug that has emerged as a potential Covid-19 treatment so far is Gilead Sciences Inc's remdesivir, a drug reserved for hospital patients.

Additional Reporting Reuters, AFP