> "There are over 20,000 prescription drug products approved for marketing."

But how does that square with the claim that the FDA has approved 1,453 drugs in its entire history?

I wonder what they mean by drug products? I'm guessing that the FDA Fact Sheet you found is counting every combo pill, extended release or sustained release form, oral vs injectible vs suppository formulation, and maybe even different dosages as different drug products.

Whereas the paper mentioning 1,453 drugs is counting only new molecular entities.

It could be, I agree. The numbers from your article seem low to me, but of course I'm not an expert. Also drugs aren't just discovered in the US, so world wide it's surely more.