Grapefruit (Citrus paradisi) is part of the citrus family of fruits and is thought to be a hybrid of sweet orange (Citrus sinensis) and pomelo (Citrus maxima). The first grapefruit tree was discovered in Barbados in the 18th century, and the fruit had yellow pulp with many large seeds at its center. Over time, several varieties have been developed, and today, grapefruits are mostly seedless with pulp ranging from white to reddish pink, depending on the content of lycopene.^[7][8][9] The characteristic aroma and bittersweet flavor of grapefruit are thanks to its content of flavonoids, terpenes, furocoumarins, simple sugars, and organic acids.^[10]

Grapefruit can be a nutritious addition to one’s diet, providing a source of vitamin C, potassium, carotenoids, fiber, and various other health-promoting vitamins, minerals, and phytochemicals.

Only a few clinical trials have examined grapefruit's health effects in humans. Some preliminary studies have pointed to potential benefits on cardiovascular health and metabolic health, including reduced blood pressure, weight loss, and improved lipid profiles and endothelial function.^{[6][11][5][4]} However, these effects aren’t found consistently, and more research is needed.

In observational studies, higher intakes of flavonoid-rich foods tend to be associated with a reduced risk of all-cause mortality, cardiovascular disease, and cerebrovascular disease (e.g., stroke).^[12][13] However, the relationship is less robust when looking specifically at grapefruit or its main types of flavonoids (flavanones). Some studies have even reported an increased risk of all-cause mortality with higher levels of consumption.^[14][15] It’s unclear why this is, but the researchers suggested it could relate to the risk of drug interactions with grapefruit or to the disproportionate consumption of fruit juice rather than whole fruit.

Although many people assume grapefruit is a harmless fruit, it actually carries some serious safety concerns that should be considered, particularly for people who take medications regularly.

Grapefruit interacts with nearly half of all oral medications. These include medications used to manage epilepsy, high cholesterol, HIV, heart arrhythmias, high blood pressure, organ transplants, anxiety, erectile dysfunction, pain, and more.^[16][17] For a list of medications that could be affected, see here. This interaction can occur with as little as 6 ounces (180 mL) of grapefruit juice or about 180 grams of fresh grapefruit and persists for at least 24 hours after consumption.^[18]

Regarding side effects, grapefruit is generally considered well tolerated when consumed in appropriate amounts. Most studies have failed to report on the adverse effects of grapefruit, apart from one study that reported both constipation and diarrhea during treatment with grapefruit capsules.^[4]

Consuming grapefruit in large amounts (≥1 liter of juice at once) seems to prolong the QTc interval (a measurement of the heart's electrical activity). This could increase the risk of torsades de pointes, a potentially fatal heart arrhythmia. This effect has been observed in multiple randomized controlled trials and appears greater in women and in people with pre-existing disease affecting the heart rhythm.^[1][2][3] The flavanone naringenin may be the culprit. In one study, QTc prolongation was observed at doses of about 1440 µmol naringenin (equivalent to roughly 390 mg). While naringenin content in grapefruit varies, this could correspond to about 4.5 whole grapefruits.^[19]

Grapefruit contains an abundance of phytochemicals with biological activity, including various flavonoids, carotenoids, and coumarins. Naringenin is the predominant flavonoid in grapefruit and is often considered the major bioactive compound.^[7] Compounds in grapefruit have been linked to various health-promoting effects, including antioxidant, anticancer, antimicrobial, anti-obesity, and antidiabetic properties.^[20][21][22]

Naringenin and a few other compounds in grapefruit activate the enzyme AMPK. AMPK helps regulate metabolism, and its activation increases the breakdown of glucose and fats and decreases their synthesis.^[23][6] This may be a driver of the antidiabetic, lipid-modulating, and weight-lowering effects of grapefruit. However, fiber and other nutritional compounds in grapefruit likely also play a role.^[6]

Grapefruit may lower blood pressure by promoting the dilation of blood vessels possibly by increasing the synthesis of nitric oxide.^[24][6]