They’ve actually done pretty recent studies and concluded you would have to get above 10 cups of coffee for it to stop being healthy.
Note that I said healthy and NOT that it would then be unhealthy. I’m bot sure how much coffee you would have to drink for that to happen, but seeing as how caffeine was misattributed to being hard on the heart and cardiovascular system, I imagine it would take a lot or like this poor young woman, you’d have to have a heart problem already.