The warning comes as GPs are being told to prescribe beta-blockers to patients with left ventricular dysfunction as part of the clinical directed enhanced service for heart failure.
Grapefruit juice is already known to boost the effects of some drugs, including statins, posing a risk of overdose.
But research presented this week at a meeting of the American Chemical Society in Philadelphia shows that taking the antihistamine fexofenadine with 300ml of grapefruit juice reduced absorption of the drug by 50 per cent.
The chemical responsible for blocking drug absorption is also found in apple and orange juice, which also have the drug-weakening effect.
Drinking up to 1,200ml of apple, orange or grapefruit juice over three hours after taking fexofenadine was found to reduce absorption of the drug by more than 70 per cent.
Medicines blocked by fruit juice include the beta-blockers atenolol, celiprolol, and talinolol, the immunosuppressant cyclosporine and the antibiotics ciprofloxacin, levofloxacin and itraconazole.
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