Grapefruit & Diclofenac

Diclofenac, medication prescribed to reduce pain and swelling, belongs to the category of drugs known as NSAIDs -- nonsteroidal anti-inflammatory drugs. This means it works to reduce inflammation and pain by stopping the body’s production of the substances that cause these symptoms. Grapefruit is known to react adversely with many medications, but diclofenac isn’t one of them.

No Known Interaction

The most recent label for diclofenac, approved by the United States Food and Drug Administration on February 23, 2011, does not list grapefruit as a substance that could react adversely with diclofenac. Additionally, MedlinePlus, a service of the National Institutes of Health, does not warn against consuming grapefruit while taking diclofenac. It is important to note that, according to the People’s Pharmacy, most medications have not yet been tested for an interaction with grapefruit. Therefore, just the fact that no interaction is specified does not mean an interaction couldn’t potentially occur.

Metabolizing Drugs

Grapefruit prevents your CYP34A enzyme from efficiently metabolizing some medications. You may effectively end up with an overdose of some medications if you combine them with grapefruit. But not all medications are dependent on your CYP34A enzyme. It plays a minor role, for example, in metabolizing diclofenac. A different enzyme -- CYP2C9 -- is largely responsible for metabolizing diclofenac. No evidence indicates that grapefruit affects your body's CYP2C9 enzyme.

Known Interactions

Diclofenac does, however, react adversely with CYP2C9 inhibitors such as the medication voriconazole. A medication called rifampin can reduce the effectiveness of diclofenac. Do not combine dicofenac with other NSAIDs, including over-the-counter medications such as aspirin. The drugs warfarin, cyclosporine, methotrexate, lithium and furosemide may also cause a negative reaction with diclofenac. Diclofenac can also reduce the effectiveness of ACE inhibitors.

Grapefruit Drug Interactions

Drugs known to interact adversely with grapefruit include birth control pills, antidepressants, statins, calcium channel blockers, anti-anxiety medications and immunosuppressants. Side effects include blood clots, stroke and heart attack. If your doctor prescribes any medication, ask if it interacts adversely with grapefruit. A single glass of grapefruit juice can slow the metabolism of some drugs by 47 percent, according to the Harvard Medical School Family Health Guide.