Does grapefruit affect the drugs you take?

If you look at the average breakfast table you’ll find many potential health hazards: coffee, breakfast cereals loaded with sugar, greasy bacon and fried eggs. So most of us would think grapefruit is a welcome nutritious addition.

But if you’re taking certain medications then you should steer clear of grapefruit. That’s because grapefruit contains a substance that interacts with a long list of drugs regularly found in medicine cabinets across the country.

Geraldine Moses, a senior pharmacist from the Adverse Medicine Events Information Line, says there is evidence that an average 200 ml glass of normal strength grapefruit juice (straight from the fruit) can cause “a clinically significant interaction with a list of drugs as long as your arm”.

Eating fresh grapefruit can also be a problem, as the compound responsible for the interaction is found in the fruit’s pulp. But Moses says eating grapefruit marmalade on toast is unlikely to cause any problems.

“There are a lot of people eating grapefruit marmalade and there is currently no evidence to say that it is causing problems, whereas there is evidence that grapefruit juice and grapefruit itself are causing problems.”

Moses says some of the drugs that interact with grapefruit include heart drugs such as statins, calcium channel blockers and amiodarone, anti-HIV medicines, and immunosuppressants.

Researchers have found the interaction is caused by a group of compounds knows as furanocoumarins (FCMs). These inhibit the metabolism of the affected drug through the small intestine or liver, which in turn increases the concentration of the drug and therefore any toxic side effects.

If you’re taking drugs that interact with grapefruit it is worth noting that some researchers have found the effects of grapefruit can last for more than 24 hours, while others have found ingesting grapefruit four hours before taking medication has no impact.

Although many pharmacists do put warning stickers on medication that interacts with grapefruit, some people still find out the hard way. Moses says this is why you need to get the latest product information from your pharmacist. You can also find a comprehensive list of drugs that interact with grapefruit on the National Prescribing Service’s website.

But it’s not all bad news, Seville oranges are the only other citrus fruit that have been reported to have similar interactions, so you can still enjoy a glass of other types of orange juice or fresh citrus fruits with your brekkie.

Geraldine Moses is a senior pharmacist from the Adverse Medicine Events Information Line. She was interviewed by Claudine Ryan. This article appeared in ABC Health News.

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