The virtues of grapefruit has been extolled for decades. It is a great source of vitamin C, potassium and lycopene and therefore finds its way onto many tables at breakfast time as a cherished accompaniment to the morning meal. But, and it is a big but, consuming grapefruit along with some chronic medicines can be potentially very dangerous.

Drug-food interaction

A medicine-food interaction occurs when some type of drink or food interferes with the way in which a medicine is supposed to work.

Grapefruit interferes with the way in which the body metabolises certain medicines. Chemicals in grapefruit stop certain enzymes that help the body to process the medicines from working properly. This can lead to dangerously high levels of the medicines in the blood, which can be very harmful and can exacerbate the side-effects of the medicine.

Grapefruit’s cousins, the pomelo and Seville orange, are believed to also cause this interaction with drugs.

No time limit

Interaction can occur up to three days after grapefruit has been consumed, so it won’t help to move the time you take either the grapefruit or the medicine. Taking less grapefruit also won’t make a difference, as you need take only very little of the grapefruit to cause the interaction.

People who take their medicines chronically are especially at risk. Ask for advice from your doctor or pharmacist if you have any concerns.

Medicines known to interact with grapefruit

    • The statins used to treat high cholesterol. Brand names include Zocor, Mevacor, Vytorin and Lipitor
    • Calcium channel blockers used to treat high blood pressure containing felodipine (Plendil and Nitrendipine), nimodipine (Nimotop), nisoldipine (Sular), nicardipine (Cardene), nifedipine (Procardia) and verapamil (Verelan)
    • Antidepressants containing buspirone and sertraline, including Zoloft and BuSpar
    • Psychiatric medicine containing triazolam (Halcion), diazepam (Valium) and midazolam (Versed)
    • Anti-seizure medicines containing carbamazepine, including Tegretol and Carbatrol
    • An HIV medicine called saquinavir (Invirase and Fortovase)
    • Drugs used to treat and prevent arrhythmias, including amidarone (Cordarone) and disopyramide (Norpace)
    • Immunosuppressant drugs containing cyclosporine (Neoral and Sandimmune) and tacrolimus (Prograf)
    • The pain medication methadone
    • The erectile dysfunction drug sildenafil, better known as Viagra.