thumb|White grapefruit juice
thumb|Chopped pink grapefruit
Grapefruit juice is the juice from grapefruits. It is rich in vitamin C and ranges from sweet-tart to very sour. Variations include white grapefruit, pink grapefruit and ruby red grapefruit juice.
Grapefruit juice is important in medicine because of its interactions with many common drugs including caffeine and medications, which can alter how they behave in the body.
Grapefruit juice is a common breakfast beverage in the United States.
Drug interactions
Grapefruit and grapefruit juice have been found to interact with numerous drugs, in many cases resulting in adverse effects. This happens in two ways: one is that grapefruit can block an enzyme which metabolizes medication, and if the drug is not metabolized, then the level of the drug in the blood can become too high, leading to an adverse effect.
Use in cocktails
Grapefruit juice is used in several cocktails, such as the sea breeze (which consists of grapefruit juice, vodka, and cranberry juice); the salty dog, the grapefruit mimosa,
Canadian regulations
Canadian regulations on commercially produced and sold grapefruit juice are that it must be made from clean, mature grapefruit and may contain sugar, invert sugar, dextrose, glucose solids and class II preservatives such as benzoic acid, amylase, cellulase and pectinase. According to Canadian standards, grapefruit juice should contain more than 1.15 milliequivalents of free amino acid per ; more than 70 milligrams of potassium per 100 ml; and have an absorbance value for total polyphenolics of no less than 0.310.