There is one huge problem with hydroxycholoroquine. It’s a 58 year old drug and it’s patent expired in 1979. ANY company can make it as a generic.
Big pharma would much prefer a trivial tweak and a new Patent starting in 2020 so they can make hundreds of billions on a new drug.
And right on cue, The politicians and doctors the pay dance like a monkey on a stick to sow stories of doubt about and restrict the use of hydroxycholoroquine.
I'd say the BIGGEST problem with it is that it CURES coronavirii, not just the novel COVID-19. That's a BIG BIG problem for the cold and flu RELIEF market.