The grapefruit was first described in the 1750s as the "forbidden fruit" of Barbados. It was introduced to Florida in the 1820s. Most grapefruit in the United States is still grown in Florida. Grapefruit juice has been used in folk medicine for the treatment of diabetes as well as to strengthen the immune system. Grapefruit is also added to cosmetics and hair care products as a fragrance.

Grapefruit has been suggested as a treatment for several conditions, but there is currently insufficient scientific evidence to support the use of grapefruit for any medical disorder. The use of supplemental grapefruit pectin in the prevention of cardiovascular disease, and the use of grapefruit seed extract in atopic eczema, warrants further scientific investigation before a strong recommendation can be made. There is conflicting research regarding the use of grapefruit for kidney stones.

Grapefruit juice is a potent inhibitor of the intestinal cytochrome P450 system (specifically, CYP3A4-mediated drug metabolism), which is responsible for the first-pass metabolism of many medications. It is via this enzyme system that grapefruit increases the effects of calcium channel blockers, benzodiazepines, immunosuppressants, and HMG-CoA reductase inhibitors.

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These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

Atopic eczema (Grade: C)
There is early, but inconclusive, evidence to support the use of grapefruit seed extract in the treatment of atopic eczema. Additional study is needed to confirm these findings.

Heart disease (Grade: C)
Grapefruit pectin supplementation may inhibit hypercholesterolemia (high cholesterol). There is promising but inconclusive human evidence to support the use of grapefruit pectin in the prevention of heart disease. Additional study is needed in this area.

Kidney stones (Grade: C)
There is limited and mixed research regarding the use of grapefruit for kidney stones. Further research is needed to clarify these results.