The warning, by the Medicines Control Agency, follows scientific research which has revealed that people taking drugs for high blood pressure, heart complaints or allergies are at risk of overdosing. The MCA says that because the juice contains psoralen, a compound also found in celery leaves, it reacts with the drugs to increase their concentration. The consequences are potentially lethal.
The warning identifies dangers with a series of drugs which are common in many households. They include the anti-histamine terfenadine, which is sold as Triludan, and the immuno-suppressant cyclosporin, which is used by transplant patients.
Also on the list are calcium channel blockers (other than amlodipine and diltiazem) which are used to treat blood pressure and angina. More than 20 million prescriptions of these CCBs, which include the popular Adalat, are issued a year.
The MCA has issued the warning through its Committee on the Safety of Medicines.
In the latest "Current Problems in Pharmaco-vigilance" briefing, the MCA warns: "Because of the potential for interactions, it is advisable for patients to avoid drinking grapefruit juice when taking the drugs indicated."
It appears that eating grapefruits poses no risk and there are believed to be no dangers from orange juice.
Research in the United States last August showed a glass of grapefruit juice could trigger an overdose. Drug firms are aware of the problems. Bayer, which makes Adalat, one of the biggest-selling CCBs, has issued warnings to patients.
Christopher Burton, chairman of the British Fruit Juice Importers Association, said there was no need for grapefruit juice cartons to carry health warnings. "It is up to the medicine manufacturers to say 'be cautious', because everybody drinks grapefruit juice and only a small number of people use the medicines where this problem arises," he said.Reuse content