Patients get warning over grapefruit

The fruit contains chemicals that can interact with certain drugs, making them more potent, with adverse effects including kidney failure, respiratory failure, internal bleeding and sudden death.

While it is well known some patients should avoid grapefruit, or grapefruit juice, the list of drugs involved has risen sharply in recent years.

Between 2008 and 2012 the number of medications with the potential to cause serious harm by interacting with grapefruit increased from 17 to 43, said scientists writing in the Canadian Medical Association Journal.

More than 85 drugs in total can interact with grapefruit, said the researchers, and the list of danger medicines includes treatments for anxiety, depression, allergy, HIV infection, seizures, heart rhythm abnormalities and high cholesterol.

A modest single helping can have an effect even if consumed hours before a drug is taken, and frequent exposure to grapefruit can make matters worse.

Combining the cholesterol-lowering drug simvastatin with a 200 millilitre glass of juice once a day for three days more than tripled its concentration level.

Older people with a reduced ability to tolerate drug overdoses were at greatest risk.