Image for grapefruit article With an outside that is shiny pink or bright yellow and an inside that drips juicy nutritional goodness, the grapefruit is one of nature’s many delicious treats. But, could this vitamin C-rich fruit be putting you in harm’s way by dangerously interacting with your medications?

The revelation that grapefruit can interact with certain medications was discovered by accident. Researchers studying ethanol’s possible effect on drug, used grapefruit juice to mask the flavor of the ethanol. The study found that the effect of the drug was increased when combined with the ethanol/grapefruit mixture. They thought this interaction was due to the ethanol. However, later studies uncovered that grapefruit juice was the true cause of the change.

The Goodness in Grapefruit

Grapefruit is a nutritionally dense food—meaning that it is an excellent source of many vitamins, but contains very few calories. Because of its superb nutritional profile, the grapefruit is a bit of a legend when it comes to diets. You may have even heard of the “Grapefruit Diet,” (although grapefruits are good for you, following the “Grapefruit Diet” is not a good way to lose weight).

Table 1 presents some of the nutritional benefits of grapefruit and grapefruit juice.

SizeCaloriesVitamin A (IU) ]]>Vitamin C]]> (mg) ]]>Potassium]]> (mg) ]]>Folate]]> (mcg)
Grapefruit, pink or red½ medium373184715915
Grapefruit, white½ medium39124017512
Grapefruit juice, pink or red, unsweetened¾ cup728157030019
Grapefruit juice, white, unsweetened¾ cup72187230018

Table 1: Nutritional content of grapefruit and grapefruit juice

How the Drug/Grapefruit Interaction Works

Cytochrome P-450 is a group of enzymes located throughout the body, with the largest amount found in the liver and the intestinal walls. This family of enzymes is responsible for making chemical reactions needed to breakdown many different compounds, from food to drugs. CYP3A4 is the most abundant member of the enzyme family. It is responsible for breaking down approximately 60% of the drugs we take.

Grapefruit—more specifically a compound in grapefruit that has yet to be identified—inhibits the activity of CYP3A4. This means that when grapefruit or grapefruit juice is consumed, a compound within the grapefruit disrupts the CYP3A4 enzyme’s ability to metabolize a drug. If a drug is not adequately metabolized, higher levels of the drug than intended may enter the bloodstream, which can lead to a potentially dangerous situation.

Grapefruit/drug interactions have been observed within a few hours after consuming grapefruit and may last for up to 24 hours. As little as eight ounces or 250 milliliters can have an effect on the metabolism of some drugs.

Give up Grapefruit?

One in five households in the US has a carton of grapefruit juice on the refrigerator shelf—and consumption is likely to increase, especially now that the juice is often ]]>calcium]]> -fortified. In light of this interaction information, would it be safer to stop drinking grapefruit juice and eating grapefruit? Although a possible drug interaction is a serious matter, giving up grapefruit may not be necessary. If you are taking any medications and you enjoy eating grapefruit or drinking grapefruit juice, it is important that you talk with your doctor. Ask specifically about the possibility of grapefruit or grapefruit juice interacting with any prescription or over-the-counter drug that you may be taking. Note that interactions can occur up to three days after eating or drinking grapefruit.

Which Drugs are Affected?

Table 2 lists medications whose blood levels can be affected by grapefruit. Even if you do not see a medication that you are currently taking on this list, it is a good idea to ask your doctor about the possibility of an interaction with grapefruit or grapefruit juice.

TypeGeneric nameBrand name
Calcium channel blockersAmlodipineNorvasc
NifedipineProcardia, Procardia XL, Adalat
QuinidineCardioquin, Quinaglute Dura-Tabs, Quinidex Extentabs, Quinora
ImmunosuppressantsCyclosporineNeoral, Sandimmune
HMG-CoA reductase inhibitorsAtorvastatinLipitor
HIV protease inhibitorsIndinavirCrixivan
SaquinavirFortovase, Invirase
Psychiatric medicationsAlprazolamXanax
CarbamazepineAtretol, Depitol, Epitol, Tegretol
DiazepamValium, Valrelease
CorticosteroidsEthinyl estradiolEstinyl, Estrace, Estraderm, Estratab, Estratest, Ogen, Premarin
ProgesteroneCrinone, Esterol 50, Prometrium
Antiparasitic agentsArtemetherArtenam
MethadoneDolophine; Methadose
MifepristoneMifeprex, RU-486

Table 2: Medications whose absorption can be affected by grapefruit