The effects of heart and cancer drugs could be wiped out if they are taken at the same time as drinking fruit juices, new research has claimed.
The evidence emerged from a Canadian study in which grapefruit juice was found to shut certain drugs out of the body. Other fruit juices, notably orange and apple, are thought to have the same effect.
Patients drinking fruit juice could be jeopardising treatments for heart disease, cancer, organ transplant rejection and infection, the scientists warned.
For 20 years it has been known that grapefruit juice can boost the potency of some drugs. But the new research, presented at the national meeting of the American Chemical Society in Philadelphia, US, shows that fruit juices can affect other drugs in the opposite way.
In tests, healthy volunteers took fexofenadine - an antihistamine used to fight allergies. They swallowed the drug with either a single glass of grapefruit juice, water containing naringin - the chemical responsible for 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.