Trump, while promoting the drug hydroxychloroquine by constantly speaking about it from his bully pulpit, denies promoting the drug hydroxychloroquine. It’s untested as a COVID-19 treatment.

In the meantime, there’s at least one (not yet peer-reviewed) mouse study suggesting that the use of hydroxychloroquine in combination with metformin (a drug often used by diabetics) can be fatal. Here’s the abstract:

“Guided by the principle of primum non nocere (first do no harm), we report a cautionary note on the potential fatal toxicity of chloroquine (CQ) or hydroxychloroquine (HCQ) in combination with anti-diabetic drug metformin. We observed that the combination of CQ or HCQ and metformin, which were used in our studies as potential anti-cancer drugs, killed 30-40% of mice. While our observations in mice may not translate to toxicity in humans, the reports that CQ or HCQ has anti-COVID-19 activity, the use of CQ resulting in toxicity and at least one death, and the recent Emergency Use Authorization (EUA) for CQ and HCQ by the US Food and Drug Administration (FDA) prompted our report. Here we report the lethality of CQ or HCQ in combination with metformin as a warning of its potential serious clinical toxicity. We hope that our report will be helpful to stimulate pharmacovigilance and monitoring of adverse drug reactions with the use of CQ or HCQ, particularly in combination with metformin.”

From “Fatal toxicity of chloroquine or hydroxychloroquine with metformin in mice“

Most doctors and scientists (unlike our politically-motivated president) would probably see such a study and exercise the precautionary principle, by reminding us that hydroxychloroquine has not been fully tested as a COVID-19 treatment. This is exactly what Fauci apparently tried to do before Trump peremptorily cut him off, in their most recent press conference.