Not 'necessarily'. Remember, it says that it also increased the QT length in healthy people. But it's not like we know if healthy people who die from long QT had just drank grapefruit juice, but deaths from long QT are pretty rare anyway. So, I don't know if we know enough to know, but it's also hard to declare it unsafe since millions of people drink it every day without any problems. Which is likely why it's still on the market and doesn't have a warning label... yet.