How Grapefruit Interacts with Medications

Grapefruit and its juice can alter how certain medications are absorbed into the bloodstream, potentially causing severe side effects or reducing the effectiveness of the medication. This interaction is primarily due to furanocoumarins—compounds in grapefruit that interfere with enzymes and proteins in the small intestine responsible for drug metabolism.

Why Grapefruit Affects Medications

Furanocoumarins disrupt the function of enzymes like cytochrome P450 3A4 (CYP3A4), a key enzyme that helps metabolize many drugs. When CYP3A4 is blocked, more of the drug enters the bloodstream and stays in the body longer, potentially leading to adverse effects. For example, blood pressure medications like nifedipine (Procardia) can cause dangerously low blood pressure when combined with grapefruit.

Examples of Medications Affected by Grapefruit:

1. Blood Pressure Medications: Grapefruit can increase levels of drugs like nifedipine, causing low blood pressure and slow heart rates.

2.Cholesterol-Lowering Statins: Statins like simvastatin (Zocor) and atorvastatin (Lipitor) can accumulate to toxic levels, leading to muscle pain and damage.

3. Immunosuppressants: Drugs such as cyclosporine (Neoral) can reach high levels, potentially harming the kidneys.
4. Anxiety Medications: Benzodiazepines like diazepam (Valium) can cause excessive drowsiness or breathing difficulties when taken with grapefruit.
5. ‘Allergy Medications: Grapefruit can decrease the effectiveness of drugs like fexofenadine (Allegra) by blocking transporter proteins needed for absorption.

Varying Effects of Grapefruit

The impact of grapefruit depends on the amount consumed and the specific medication taken. Even small amounts, such as one grapefruit or an 8-ounce glass of juice, can significantly alter drug metabolism.

Other Fruits to Watch Out For

Besides grapefruit, fruits like Seville oranges, tangelos, and pomelos also contain furanocoumarins and should be consumed with caution. Additionally, citric acid in citrus juices can reduce the effectiveness of certain drugs, like the osteoporosis medication alendronate (Fosamax).

Advice for Patients

Always check the medication information leaflet for potential food interactions, and consult your doctor or pharmacist to ensure grapefruit won’t interfere with your medications.

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