Theragenomic Community Wisdom: Grapefruit Can Interact With Drugs. Better Be Safe Than Sorry.

Last Updated on May 26, 2014 by Joseph Gut – thasso

May 24, 2014 – There is a ever rising number of drugs that can be risky when taken with grapefruit due to the an increase of new medications that share some critical metabolic pathways on a particular drug metabolising enzyme (CYP3A4 to be precise) with grapefruit.

As it stands, there are now more than 85 drugs that may interact with grapefruit. The number of drugs that may result in potentially fatal side effects when mixed with grapefruit increased from 17 to 43 during the past four years. This equates to more than six new potentially risky drugs a year. The list includes some statins hat lower cholesterol such as atorvastatin, lovastatin and simvastatin, some antibiotics, cancer drugs, and heart drugs. Most at risk are older people who use more prescriptions and buy more grapefruit.

Here’s what happens: Grapefruit contains furanocoumarins, which block an enzyme that normally breaks down certain medications in the body. When it is left unchecked, medication levels (i.e., systemic exposure) can grow to high in the patients body and reach levels that may cause serious, if not fatal drug adverse reactions.

It’s not just grapefruits, either. Other citrus fruits such as Seville oranges (often used in marmalade), limes, and pomelos also contain the active ingredients (furanocoumarins), but have not been as widely studied as grapefruit.

Grapefruit and Some Medications: Risky Business

Researchers searched the medical literature for articles on grapefruit and drug interaction using key terms. The degree of the grapefruit effect can vary. With some drugs, just one serving of grapefruit can make it seem like a person is taking multiple doses of the drug. This interaction can occur even if grapefruit is eaten many hours before taking the medication. For example, simvastatin, when taken with about a 7-ounce glass of grapefruit juice once a day for three days, produced a 330% greater concentration of the drug compared to taking it with water. This can cause life-threatening muscle damage called rhabdomyolysis.

Grapefruit and grapefruit products may interact with a broad class of medications ranging from cardiovascular to hormonal drugs. Some have more of an effect if you take them in close proximity to drinking grapefruit juice than if you space it out, but there can still be an interaction if you take the pill the night before or 12 hours before consuming grapefruit or grapefruit juice.


Ph.D.; Professor in Pharmacology and Toxicology. Senior expert in theragenomic and personalized medicine and individualized drug safety. Senior expert in pharmaco- and toxicogenetics. Senior expert in human safety of drugs, chemicals, environmental pollutants, and dietary ingredients.