I don't know what to believe any more because that article says kale is a low oxalate food, but https://blog.swedish.org/swedish-blog/kale-causes-kidney-sto... says the opposite (and was on the list I got at discharge)

As far as I understand it, the interaction of Grapefruits with for example statins is because it has Furocumarine, but that isn't unique to it. Other citrus fruits have it as well. It's just that Grapefruit isn't as sour and it's consumed in much higher doses compared to say lemon juice.