Grapefruit in Your Diet may Interfere with Certain Medications

The Statue of Liberty on Liberty Island in New York Harbor. (Dr. Noorali Bharwani)
The Statue of Liberty on Liberty Island in New York Harbor. (Dr. Noorali Bharwani)

“Our research group discovered the interaction between grapefruit and certain medications more than 20 years ago,” says an article in the Canadian Medical Association Journal (CMAJ March 5, 2013) written by Dr. David Bailey, Ph.D and his colleagues from Ottawa.

Certain other citrus fruits and products can interfere with several kinds of prescription pills. You are advised to check with your pharmacist and/or doctor before consuming any citrus products, including grapefruit, if you take prescription medications. Taking your medication and grapefruit product at different times does not stop the interaction.

Chemicals in the fruit can interfere with the enzymes that break down the medication in the digestive system. As a result, the medication may stay in your body for too short or too long a time. A medication that’s broken down too quickly won’t have time to work. On the other hand, a medication that stays in the body too long may build up to potentially dangerous levels.

There is a long list of medications that is affected by grapefruit and other citrus food. Here are some examples:

Antibiotics: erythromycin

Cholesterol reducing pills: atorvastatin (Lipitor), lovastatin (Altoprev), others

High blood pressure pills: felodipine, carvedilol (Coreg), others

Pills for heart problems: amiodarone (Coradarone, Pacerone)

Antidepressants: diazepam (Valium, Diastat), fluvoxamine, others

Pills to prevent organ rejection in transplant recipients: cyclosporine (Sandimmune and others)

Play it safe with prescription drugs. Always ask your doctor or pharmacist when you get a new prescription if it interacts with any foods or other medicines.

Many of the drugs that interact with grapefruit are highly prescribed and are essential for the treatment of important or common medical conditions. Currently, more than 85 drugs have the possibility of interacting with grapefruit; of these drugs, 43 have interactions that can result in serious adverse effects.

The chemicals in grapefruit involved in this interaction are the furanocoumarins.

One whole grapefruit or 200 mL of grapefruit juice is sufficient to cause clinically relevant increased systemic drug concentration and subsequent adverse effect. Seville oranges, often used in marmalades, limes and pomelo also produce this interaction.

In spite of the scientific evidence from reliable sources regarding adverse effects as discussed earlier, in routine clinical practice physicians do not see too many complications. One reason could be that multiple factors likely need to combine to achieve a marked increase in systemic drug concentration. It is reasonable to assume that just exposure to any interacting combination would not be sufficient to cause a clinically important change in drug response in all, if not most, cases.

Having said that, the fact remains you have to be vigilant. Pharmacists are the best source of information when it comes medications.

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