The short answer: Most of the studies done to this point are severely limited, and there are better ones still in progress. Ideally we’d all hope for good results but not turn this life-or-death question into a ridiculous political argument, but I suppose that opportunity has already passed.
Both USA Today and the New York Times have decent summaries of the research. The NYT nicely explains why so many people have thought the drug showed promise and why some medical professionals are using it on patients:
A promising laboratory study, with cultured cells, found that chloroquine could block the coronavirus from invading cells, which it must do to replicate and cause illness. . . . Reports from doctors in China and France have said that hydroxychloroquine, sometimes combined with the antibiotic azithromycin, seemed to help patients. But those studies were small and did not use proper control groups. . . .
A study from China did include a control group and suggested that hydroxychloroquine might help patients with mild cases of Covid-19, the disease caused by the coronavirus. But that study had limitations: It was also small, with a total of 62 patients, and they were given various other drugs as well as hydroxychloroquine. The doctors evaluating the results knew which patients were being treated, and that information could have influenced their judgment. Even if the findings hold up, they will apply only to people who are mildly ill.
But other studies are a lot less promising. From USA Today:
A study posted on April 23 involving 368 patients with confirmed cases of COVID-19 treated at Veterans Health Administration medical centers found there were more deaths among those given hydroxychloroquine than those receiving standard care. In addition, the drug made no difference in the need for ventilators.
Another study from earlier this month found “no significant association between hydroxychloroquine use and intubation or death,” though it also had very wide confidence intervals, meaning it didn’t rule out substantial effects in either direction.
The bottom line is that we need large, randomized trials with proper control groups to know what difference this drug makes. Several such studies are in the works.
I don’t envy doctors who have to decide right now whether to use this drug on the patients in front of them. But if you’re not a doctor, just wait for the answer!