from Mayo Clinic article:
Grapefruit and certain other citrus fruits, such as Seville oranges, can interfere with several kinds of prescription medications.
Don't take these interactions lightly. Some can cause potentially dangerous health problems. If you take prescription medication, ask your doctor or pharmacist whether your medication interacts with grapefruit or other citrus products.
You may need to eliminate grapefruit products from your diet. Simply taking your medication and grapefruit product at different times doesn't stop the interaction. Alternatively, you can ask your doctor if there's a comparable medication you can take that doesn't interact with grapefruit.
Problems arise because chemicals in the fruit can interfere with the enzymes that break down (metabolize) the medication in your digestive system. As a result, the medication may stay in your body for too short or too long a time. A medication that's broken down too quickly won't have time to work. On the other hand, a medication that stays in the body too long may build up to potentially dangerous levels.
The list of medications that can interact with grapefruit includes commonly prescribed medications that:
Fight infection
Reduce cholesterol
Treat high blood pressure
Treat heart problems
Prevent organ rejection
Treat anxiety
Control seizures
Minimize motion sickness
Treat erectile dysfunction
Replace hormones
Reduce cough
Control pain
Another potential problem is that some foods and drinks may contain grapefruit but don't say so in the name or on the ingredients list. For example, numerous citrus-flavored soft drinks contain grapefruit juice or grapefruit extract.
Play it safe with prescription drugs. Always ask your doctor or pharmacist when you get a new prescription if it interacts with any foods or other medicines. If the answer is yes, ask whether you need to eliminate that food from your diet.
