A new study examining the impact of fruit juice consumption on the efficacy of prescription drugs reveals that some drugs — including heart and cancer drugs, antibiotics and hayfever medications — can lose virtually all of their benefit if they are washed down by juice.

Reports the London Daily Mail: “Orange, apple and grapefruit juice can … stop drugs from entering the bloodstream and getting to work in the body — possibly rendering them useless … The potential effects are so serious, researchers warned, that if in doubt, patients should swap fruit juices for water when on medication.”

A wide variety of drugs were affected by fruit juice consumption:

Drugs shown to be weakened … include the blood pressure-lowering beta blockers atenolol, celiprolol, and talinolol and the hay-fever treatment fexofenadine. The multi-purpose antibiotic ciprofloxacin, used to combat germs behind food poisoning and bone and joint infections, is also affected. So is the cancer drug etoposide and a drug given to prevent the rejection of transplanted organs…

Even fruit juice consumed two hours before taking a pill can undermine a drug’s efficacy, the study showed. Advises researcher David Bailey:

Juice taken four hours prior to drug intake did not have an effect. Thus, it should be possible still to take grapefruit, orange and apple juices while on affected medications provided there is a sufficient time interval. I would recommend taking drugs with water on an empty stomach to get the most consistent effect.

While we like to think our doctors and pharmacists are staying abreast of the latest research and will tell us if the medication we’re on will be affected by fruit juice, my philosophy is better safe than sorry. Drink more water — it’s good for you.