How does grapefruit juice affect medicines?

Grapefruit juice contains chemicals that can cause problems with enzymes that break down certain types of medicines in your intestines. When a medicine does not get broken down properly in the intestines, you can end up with too much medicine in your blood. Having too much medicine in your blood increases your chances of having serious side effects.

Which medicines are affected by grapefruit juice?

Most medicines are not affected by grapefruit juice. But more than 50 medicines are affected by grapefruit juice. These include medicines for:

Abnormal heart rhythm.
Allergies.
Anxiety.