THE FRENZY over the antimalarial drug hydroxychloroquine is probably not the last time someone will dangle the prospect of a miracle cure for covid-19. More wild claims and false starts can be expected. That is why it is important to grasp the lessons of President Trump’s reckless recommendation of a drug without evidence of efficacy. Especially at a time of grave distress, the lesson is: Demand evidence, seek proof and don’t listen to quacks anywhere.

Mr. Trump carelessly broadcast enthusiasm for the drug March 21, declaring that hydroxychloroquine and the antibiotic azithromycin “have a real chance to be one of the biggest game changers in the history of medicine.” He suggested they be put in use “immediately,” and the Food and Drug Administration authorized emergency use against covid-19. Mr. Trump’s enthusiasm was based on a tiny study in France. The drug, approved for use against malaria and some other maladies, has known side effects, including altering the heartbeat in a way that can lead to death. The frenzy caught the imagination of French President Emmanuel Macron, who flew to Marseille to meet Didier Raoult, the scientist who championed the drug and has become something of a folk hero in France.

Now, reality is settling in. Rick Bright, director of the Biomedical Advanced Research and Development Authority, said Wednesday he was forced out of his job because he balked at broad use of the drug, “promoted by the administration as a panacea, but which clearly lack[s] scientific merit.” A preliminary study, not yet peer-reviewed, and funded by the National Institutes of Health and the University of Virginia, looked at 368 patients in Veterans Affairs medical centers who were ill with covid-19. The researchers found “no evidence that use of hydroxychloroquine, either with or without azithromycin, reduced the risk of mechanical ventilation” in the sick patients. Nearly 28 percent of those who got the hydroxychloroquine died, and 22.1 percent of those with the combination died, while only 11.4 percent died among those who got neither.

Separately, a panel made up of prominent U.S. government agencies and professional medical associations recommended against the use of hydroxychloroquine and azithromycin — Mr. Trump’s “game changer” — because of “the potential for toxicities.” The panel said there is “insufficient clinical data to recommend either for or against” hydroxychloroquine alone. These research reports confirm that before anyone declares these drugs a cure, they must be subject to a rigorous clinical trial.

The United States has built a process of drug testing and approvals considered the gold standard around the world, involving three phases of clinical trials to test safety, dosage, efficacy and possible side effects of a new drug or vaccine. The fear inspired by the coronavirus must not undermine this rigorous procedure. Ultimately, a new drug or vaccine needs public confidence. Shaking that trust with premature and unsubstantiated claims will lead only to more misery and suffering.

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