Nearly 15,000 of the 96,000 patients in the analysis were treated with hydroxychloroquine or chloroquine alone or in combination with a type of antibiotics known as a macrolide, such as azithromycin, within 48 hours of their diagnosis.

The difference between patients who received the antimalarials and those who did not was striking.

For those given hydroxychloroquine, there was a 34 percent increase in risk of mortality and a 137 percent increased risk of a serious heart arrhythmias. For those receiving hydroxychloroquine and an antibiotic — the cocktail endorsed by Trump — there was a 45 percent increased risk of death and a 411 percent increased risk of serious heart arrhythmias.

Those given chloroquine had a 37 percent increased risk of death and a 256 percent increased risk of serious heart arrhythmias. For those taking chloroquine and an antibiotic, there was a 37 percent increased risk of death and a 301 percent increased risk of serious heart arrhythmias.

Cardiologist Steven Nissen of the Cleveland Clinic said the new data, combined with data from smaller previous studies, suggests that the drug “is maybe harmful and that no one should be taking it outside of a clinical trial.”