Online demand for the anti-malaria drug hydroxychloroquine surged by more than 1,000% after Donald Trump endorsed it as a potential treatment for Covid-19 without providing evidence it worked, a new study has found. There are no proven prescription therapies to treat Covid-19, the disease caused by the coronavirus. Despite the lack of evidence, the presidential endorsement drove up online searches for buying hydroxychloroquine, and its chemical cousin chloroquine, by 1,389% and 442% respectively. Internet searches remained high, researchers said, even after NBC News reported an American couple had accidentally poisoned themselves by taking a liquid containing chloroquine meant to treat parasites in fish tanks, following a Trump press briefing in which he promoted the drug. "We know that high-profile endorsements matter in advertising, so it stands to reason that these endorsements could spur people to seek out these medications," said Michael Liu, a graduate student at Oxford University and the studys first author, in a statement. The research was published as a letter in the Journal of the American Medical Association Internal Medicine. The authors looked at the prevalence of internet searches using the terms "buy", "order", "Amazon", "eBay" or "Walmart" in combination with "hydroxychloroquine" or "chloroquine". Researchers examined searches before and after two prominent endorsements, the first on 16 March by the tech billionaire Elon Musk, who tweeted about chloroquine, and the second on 19 March by Trump, who endorsed hydroxychloroquine in combination with the antibiotic azithromycin at a press conference. "The first and largest spike in searches corresponded directly with Musks tweet and Trumps first televised endorsements," authors wrote. "These changes represent about 93,000 and 96,000 more searches than expected for chloroquine and hydroxychloroquine, respectively, with 216,000 total searches for both drugs over just 14 days." "Musks and Trumps endorsements are especially troublesome for three reasons," said Liu. "First, these treatments have inconclusive clinical efficacy. Second, these drugs have potentially fatal side-effects. Third, chloroquine-containing products such as aquarium cleaner are commercially available to the public without a medical prescription." Misinformation about health is usually thought of as coming from "unreliable health sources, online trolls and bots", said Dr Mark Dredze, a study co-author and associate professor at Johns Hopkins University, in a statement. "Its rare to have health misinformation coming from such high-profile figures." Since the endorsements by Trump and Musk, the US Food and Drug Administration has issued a warning about potentially life-threatening cardiac side-effects associated with chloroquine and hydroxychloroquine. The warning came after a small Brazilian study was stopped by safety advisers, because patients treated with a high dose of chloroquine appeared to die at twice the rate of those treated with a lower dose of the drug. Despite the dangers to the public, Trump has gone on to make other potentially harmful suggestions for treatments, including injecting disinfectant. The bizarre comment prompted several disinfectant companies and Harvard experts to urge people: "Please do not inject bleach or disinfectant." The research authors called on government and drug companies to begin "actively mitigating the negative consequences of this misinformation" and for Google and other internet companies to expand education efforts. "The FDA and other agencies are there to protect the interests of public health, and they need to be there now," said John Ayers, University of California San Diego professor of medicine. "We found hundreds of thousands of people were motivated to go out and try to buy these products online," he said. "There werent aware of it, they werent interested in it - they were trying to buy it." Despite the concerns, doctors have started "widely" prescribing the drugs. That demand has led to a shortage for patients who already take the drugs, predominantly women and people of color with autoimmune conditions, an editorial accompanying the research said. "Given the toll of COVID-19, the pressure to do something is enormous and understandable," wrote Drs Colette DeJong and Robert Wachter of the University of California San Francisco department of medicine, in a related comment article. "But that must not prompt clinicians to jettison the tenets of evidence-based medicine and the admonition to do no harm."