There is no such study, in my view. I read the pre-print literature every day, and then I track and cut citations from the actual publications.
All of the double blind studies show that HCQ is either ineffective or actually harmful.
The "big study" of many patients was a retrospective study in which there were no controls over what
other medications people got, aside from HCQ and Z-pac. In fact, many of the patients got other treatments, including one we know to be effective (steroids) at managing the cytokine storm. Also, some patients got Zinc, which is now thought to be effective and is especially important in the way HCQ works. The antivirals, studied in the same way (retrospectively), as well as interferon are very effective, but not HCQ.
So even in a poorly constructive retrospective study, HCQ barely made a difference. In double blind studies, HCQ is shown not to work, which is why the FDA withdrew its provisional approval: several US double blind studies show exactly what double bind studies in other nations do: no positive outcomes to HCQ.
Compare that, for example, to similar studies done on other drugs/compounds that show they
do work. Here's yet another in the very long string of articles about how critically ill Co-Vid patients have markedly lower Vitamin D levels (a known issue in the United States - which would take a few pages here to describe the etiology and incidence):
Vitamin D insufficiency as a potential culprit in critical COVID-19 patients - PubMed
Here are some double blind studies on HCQ:
Hydroxychloroquine is not indicated for COVID-19 under any circumstances
Large study finds hydroxychloroquine Covid-19 treatments linked to greater risk of death and heart arrhythmia (MSM article but has citation to Lancet which is available online)
Here's one of the larger blind studies (they did three groups, so as to study HCQ with and without Z-Pac):
https://www.nejm.org/doi/full/10.1056/NEJMoa2019014
And here's another one (smaller - there are a dozen like it):
A Cluster-Randomized Trial of Hydroxychloroquine as Prevention of Covid-19 Transmission and Disease
There was enough data for WHO to halt use of it:
WHO halts hydroxychloroquine trials after failure to reduce death
What all this talk about HCQ has done is tout an ineffective, potentially harmful treatment and push the many other candidates out of public view.
One of the most important things a person can do, if they get CoVid, is to be able to converse with doctors about possible treatments. A person who asks for HCQ is going to be given something else, obviously, but it limits real dialogue between doctor and patient. Since many patients who are going into the hospital have the biomarkers associated with high risk for falling into a critical state, it is crucial to be able to communicate while the patient is still conscious and in their right mind (people with low oxygen levels are not full participants in their care from the beginning - so it's important for a family advocate to know what real treatments are).
Yet, here on WS, we long ago stopped discussing treatments, except that HCQ keeps grabbing attention. There are better antivirals on the market (perhaps better than remdesivir), there are other treatments (too many for me to summarize all at once - but
@margarita25 has been diligent in posting about nearly all of them).
If we want to revive a discussion on what actually works for CoVid, we need to leave HCQ permanently behind. Here's the explanation on why the FDA has abandoned it (very large double blind/triple blind studies):
https://www.fda.gov/media/138946/download