Anyone taking medication should beware of drinking fruit juice, Canadian researchers have found.

Grapefruit, orange and apple juice can all have a significant effect on the uptake of drugs — either lowering or increasing their effectiveness.

While the influence of grapefruit juice is already well known, and some drug labels caution against drinking it with medicines, the latest research has extended the need for care.

Results presented to the American Chemical Society meeting in Philadelphia yesterday by David Bailey, Professor of Physiology, Pharmacology and Medicine at the University of Western Ontario, show that fruit juices can limit the effects of several drugs, including three beta-blockers used to treat high blood pressure, the cancer drug etoposide and some antibiotics.

In tests, healthy volunteers took fexofenadine, an antihistamine. They swallowed the drug with either grapefruit juice, water containing naringin — the chemical that causes the fruit’s bitter taste — or plain water. When the medicine was taken with grapefruit juice, only half as much of the drug was absorbed into the body as it was with water.

Naringin and similar substances in orange and apple juices appeared to block a “transporter” molecule called OATP1A2 which helped to shuttle drugs from the small intestine to the bloodstream.

Drugs whose levels in the body were boosted by grapefruit juice were affected by a different mechanism that prevented them being broken down.

Professor Bailey originally discovered the drug-boosting effects of grapefruit 20 years ago. He said: “I’m sure we’ll find more drugs that are affected in this way.” Most medicines should be taken only with water, he said.

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