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Effect of Grapefruit Juice on Paracetamol

By Dorian Facey ; Updated July 18, 2017

White, pink and ruby red varieties of grapefruit yield a tangy, flavored juice that many people enjoy. Using juice to take pills is common practice, but medical research has shown that grapefruit juice is not a wise choice for taking some medications because it can lead to dangerous levels of the medicine in your body. Paracetamol is another name for acetaminophen, and the absorption rate of the drug is affected by grapefruit juice.

The Grapefruit Juice Habit

The interaction between grapefruit juice and drugs was discovered inadvertently when the juice was used to mask the flavor of ethanol in a 1989 drug experiment. Ten years later, the journal “Experimental and Toxicologic Pathology” reported a study where mice were given either small amounts of grapefruit juice for 10 days before an experiment involving paracetamol, or a single, larger dose 90 minutes prior to the ingestion of paracetamol. The researchers found that long term, repeated ingestion of grapefruit juice had a greater effect on paracetamol than a single dosage.

Experimental Evidence

The “Journal of Medicinal Food” published a 2008 study that recorded the effect of grapefruit juice on acetaminophen absorption in mice. Two hundred microliters of white or pink grapefruit juice was fed to mice, followed in an hour by 10, 50 or 100 mg/kg of acetaminophen. The concentration of acetaminophen in the mice was tested after one and two hours. It was noted that white grapefruit juice caused an increase in acetaminophen in the mice after one hour, while pink grapefruit juice caused an increase after two hours.

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Grapefruit Juice and Drug Interactions

The rate at which an ingested drug is metabolized is usually reflected in the recommended dosage and prescribed frequency. The amount of drug in the blood can be altered if the drug is metabolized differently than expected. Grapefruit juice inhibits the cytochrome P - 450 3A4 enzyme system in the intestine that regulates the first phase of metabolism for some drugs. It is also thought to inhibit the P-glycoprotein pump in the intestinal wall that transports substrates for this enzyme system. Both situations lead to increased concentration of the drug in your blood, which could be dangerous. The scientific evidence points to paracetamol, or acetaminophen, being one of the drugs affected by grapefruit juice.

Considerations

Various research groups have reported that grapefruit juice is beneficial in treating and preventing a range of medical conditions, including atherosclerosis and cancer, making it an attractive drink choice for many people. Since the scientific evidence indicates that this juice could interact with your medication, it may be wiser to choose a different lubricant to ease the passage of your paracetamol or other pills down your throat. Research shows that white grapefruit juice appears to have a more immediate effect on paracetamol concentration than pink grapefruit juice, hence pink grapefruit juice may be the less problematic of the two when taking this drug. Talk to your doctor if you are unsure about the interaction between your foods and medication.

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