Is grapefruit dangerous?

FORBIDDEN FRUIT? Studies have found that grapefruit juice can interact with several medications.
FORBIDDEN FRUIT? Studies have found that grapefruit juice can interact with several medications.

Grapefruit - friend or foe?

''For a number of years my husband and I have been enjoying grapefruit in all its glorious taste and colour. However, some of our friends will avoid grapefruit at all costs - whole, as juice, or even in marmalade. This is because they have been prescribed medication with the words ''Avoid grapefruit and its juice'' on the label. Can you give us the true story?'' - Gloria

Tart, tangy, with an underlying sweetness, grapefruit are delicious, especially now when they are at their best. Packed full of goodies, including vitamin C, vitamin A, vitamin B, magnesium, potassium, folic acid and the antioxidant lycopene, they can be a fabulously healthy addition to your diet.

However, during the last few years there has been increasing adverse publicity for the grapefruit.

Studies have found that its juice can interact with several medications, and these findings are probably applicable to the fresh fruit as well.

The research behind this was looking at the potential interaction of alcohol with a blood pressure drug called felodipine.

They found that blood levels of felodipine were markedly higher than they expected, and tracked it back to the grapefruit juice that had been used to mask the taste of the alcohol.

This accident of science has led to further research to try to ascertain exactly what it is about grapefruit that can be hazardous, and which medications might be affected.

What we know to date, and this could change in the future, is that compounds in grapefruit called furanocoumarins block certain enzymes in the gut. These enzymes are responsible for breaking down some medications, so if their effect is blocked the result can be potentially dangerously high levels of the drug being absorbed into the blood stream.

Higher levels of a drug can lead to a greater risk of side effects and toxicity, so it is not an interaction to be taken lightly.

The ''grapefruit effect'' is highest within four hours of ingesting the fruit, but can last for up to 24 hours, so certain medications mean that you need to avoid grapefruit completely.

A similar effect has been found with seville oranges, not usually consumed for their juice as they are quite sour, but highly sought after by marmalade fans. Marmalade can also contain differing quantities of grapefruit, and it is impossible to standardise the amount of furanocoumarins that might be present in a serving. Some people advocate avoiding it completely, but I suspect that regular consumption of a small amount of marmalade, for example, one to two teaspoons, may be safe, depending on the type of medication you are on.

The medications involved include:

- Felodipine - the original drug studied.

- Cyclosporin - a chemotherapy agent, also used to treat some types of arthritis and connective tissue disease.

- Simvastatin and atorvastatin - cholesterol-lowering drugs.

- Primaquine -an antimalarial.

- Tacrolimus - an immunosuppressant often used after organ transplants.

- Buspirone - used to treat anxiety.

- Carbamazepine - used for epilepsy, bipolar and chronic pain.

- Dextromethorphan - a type of analgesia.

- Amiodarone - used to treat abnormal heart rhythms.

Nifedipine, verapamil and related drugs - used for angina, heart rhythm and blood pressure problems.

If grapefruit or its juice is consumed with any of these medications, there is a risk of increasing blood levels of the drug by two to nine times their usual concentration, which can be extremely dangerous.

There are other drugs where there is a potential reaction, but it is thought to be much less hazardous and probably of little practical relevance. These drugs include:

- Benzodiazepines - such as valium, triazolam and midazolam, used to treat anxiety and insomnia.

- Digoxin - for problems with heart rhythm.

- Erythromycin - an antibiotic.

- Fexofenadine - an antihistamine, used for allergies and hayfever.

- Fluvoxamine and sertraline - antidepressants.

It is much less important to completely avoid grapefruit if you are on one of these, and you can in all likelihood cautiously consume a small quantity without any harmful effects.

I suggest you discuss this fully with your doctor or pharmacist first.

But it is not all doom and gloom for your friends, Gloria.

If they are not taking any medication on the list above, they are free to enjoy grapefruit. However, if they have been prescribed one of those drugs, they may need to wait a few years, but the word from the United States is that a hybrid pomelo-grapefruit is being developed.

This should give you all the taste and goodness of grapefruit, with none of the risks.

- Cathy Stephenson is a general practitioner, medical forensic examiner and mother of three. If you have a question for her, email

The Dominion Post