Dunno.
If they had side effects they would probably quit taking them.
The theoretical concern is side-effects specifically combined with this particular disease, both generally and at certain stages - like Rye Syndrome’s relationship with Aspirin. Both the broad concept of side-effects, as well as development of specific dosages need to be performed.
Before universally giving out a treatment, one should always keep in mind at least the possibility of a universal screwup.
It isn’t as if research with covid viruses with chloroquine hadn’t already been done.
I don’t see the problem you suggest remaining unknown up to this point as a worth worrying about.
https://virologyj.biomedcentral.com/articles/10.1186/1743-422X-2-69
They researched the matter fifteen years ago when we didn’t have a worldwide pandemic and they could go about it in a leisurely fashion.