Below are multiple scientific studies found in medical journals that showed positive results from treating patients with HCQ:
U.S. https://www.medrxiv.org/content/10.1101/2021.05.28.21258012v1
This U.S. observational study preprint published May 28,2021
reevaluated 255 mechanically ventilated patients early on in the
pandemic when hydroxychloroquine was still allowed. The survival rate
of those on hydroxychloroquin increased to between 200% to 300% over
the control group.
Spain: https://www.medrxiv.org/content/10.1101/2020.07.17.20155960v1
In a large Spanish study involving thousands of patients admitted with COVID-19, hydroxychloroquine and prednisone administration was found to be associated with improved outcomes. Other treatments were associated with no effect or worse outcomes.
Italy: https://www.ejinme.com/article/S0953-6205(20)30335-6/fulltext
Italian study involving 3,451 participants that showed hydroxychoroquine use was associated with a 30% lower risk of death in COVID-19 hospitalized patients.
France: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7315163/
French study found that early diagnosis, early isolation and early treatment of COVID-19 patients, with at least 3 days of HCQ-AZ lead to a significantly better clinical outcome and a faster viral load reduction than other treatments.
South Korea: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7162746/
After a large COVID-19 exposure event in an LTCH (Long Term Health Care) in Korea, PEP (post-exposure prophylaxis ) using hydroxychloroquine (HCQ) was administered to 211 individuals, including 189 patients and 22 careworkers, whose baseline polymerase chain reaction (PCR) tests for COVID-19 were negative. PEP was completed in 184 (97.4%) patients and 21 (95.5%) careworkers without serious adverse events. At the end of 14 days of quarantine, all follow-up PCR tests were negative.
China: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7135139/
Study showed that chloroquine could reduce the length of hospital stay and improve the evolution of COVID-19 pneumonia, leading to recommend the administration of 500 mg of chloroquine twice a day in patients with mild, moderate and severe forms of COVID-19 pneumonia. Researchers said “the activity of hydroxychloroquine on viruses is probably the same as that of chloroquine since the mechanism of action of these two molecules is identical, and we are used to prescribe for long periods hydroxychloroquine, which would be therefore our first choice in the treatment of SARS-CoV-2.“
India: https://pubmed.ncbi.nlm.nih.gov/32205204/
Researchers found that hydroxychlroquine decreases the duration of viral shedding. In their study, they said “We believe that the hydroxychloroquine prophylaxis in selected groups of high-risk contacts is a prudent approach considering the risk–benefit analysis”
While there may be other drugs better suited to treat COVID-19,
these studies referenced above were not made known to the general
public by most media outlets as hydroxychloroquine became highly
politicized in 2020.
Studies that say hydroxychloroquine is not effective in treating COVID-19:
There are also studies that found HCQ did not work in treating
COVID-19; however, as shown in the links below these studies were done
on patients who were severely ill. HCQ appears to work best on patients
in early stages of disease or as preventative to disease after
exposure.
https://www.acpjournals.org/doi/10.7326/M20-4207
https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa1009/5872589
The largest study that said Hydroxychloroquine was ineffective (which
ended up being retracted) was the study
published in the Lancet that involved over 96,000 participants from
around the world. This was also the most controversial study on
hydroxychloroquine and COVID-19 in the world. Questions about the
research methodology surfaced right after the study was published. The
Lancet launched a third-party peer review. The company that
ran the study, Surgisphere Corporation, would not provide full access
to the information for a third-party peer review so the Lancet ended up
retracting the study.
Before it was retracted however, it had already resulted in almost
all hydroxychloroquine studies being stopped. Just days after being
published in the Lancet, the World Health Organization (WHO) and the UK
Medicines and Healthcare products Regulatory Agency (MHRA) instructed
organizers of clinical trials of hydroxychloroquine as a COVID-19
treatment or prophylaxis to suspend recruitment. The French government reversed an earlier
ruling which had allowed hydroxychloroquine to be prescribed to
patients hospitalized with the virus.
You can read more about the Surgisphere study “scandal” here: https://www.the-scientist.com/features/the-surgisphere-scandal-what-went-wrong–67955.