To be clear, the UK is undergoing a clinical trial with hydroxychloroquine. Hopefully it works, but as of now it's not known if the harms outweigh the benefits.
https://www.theguardian.com/world/2020/may/19/uk-to-test-hyd...
I have no idea if this medicine will have any impact but at this point, I've seen so many people claim it's some sort of quack medicine/conspiracy/etc that it's important people realise that it's being taken seriously. As far as I can tell the moment Trump mentioned it a huge number of people decided it must, inherently, be wrong and have been wrongly attacking it ever since.