https://en.wikipedia.org/wiki/Naringin

This is a toxic flavonoid found in a variety of common fruits. It has been well known since the mid 80s when grapefruits became known for killing elderly people in nursing homes. Last year the FDA posted an advisory not to drink any fruit juice with powerful medications.

I remember this came up in conversation last year on HN when people were deeply offended when I pointed out that eating gold, an extreme heavy metal, is toxic especially with certain food combinations and then a week later reading about the FDA advisory on CNN.