… researchers warn.
Researchers at the Lawson Health Research Institute in London, Ontario, are warning people, especially those over 45, who are on medication to be cautious about using grapefruit or the juice, especially those older than 45. They say more prescription drugs are available that can interact with grapefruit juice with potentially serious effects including sudden death.

Grapefruit juice is known to interact with some types of medications, leading to an overdose hazard.

David Bailey, a clinical pharmacologist at the London Institute reviews new product monographs and prescribing information for the Canadian Pharmacists Association. He monitors those with the potential to produce serious adverse reactions.

“What I’ve noticed over the last four years is really quite a disturbing trend, and that is the increase in the number of drugs that can produce not only adverse reactions but extraordinarily serious adverse drug reactions,” Bailey told the CBC. He added that “between 2008 and 2012, the number of drugs in the list has gone from 17 to now 44.”

Many of the drugs are common. These include some cholesterol-lowering statins, antibiotics and calcium channel blockers used to treat high blood pressure and agents used to fight cancer or suppress the immune system in people who have received an organ transplant. People older than 45 buy the most grapefruit and take the most prescription drugs, making this group the most likely to face interactions, researchers said in an article published in a recent edition of the Canadian Medical Association Journal, titled “Grapefruit-medication interactions: forbidden fruit or avoidable consequences?”

The researchers added that older adults also tend to be less able to compensate when faced with excessive concentrations of drugs compared with young and middle-aged people—another reason that those over 45 seem to be particularly vulnerable.

“Taking one tablet with a glass of grapefruit juice is like taking 20 tablets with a glass of water,” Bailey said. “This is unintentional overdosing. So it’s not surprising that these levels go from what we call therapeutic to toxic.”

The researchers noted that all sources of grapefruit—the whole fruit or 200 ml of grapefruit juice— and other citrus fruit such as Seville oranges (often used in marmalade), limes and pomelos can lead to drug interactions.

The researchers want to get the word out that the interaction can occur even if someone eats grapefruit or drinks the juice hours before taking a drug, such as downing the drink at breakfast and taking the medication after dinner.