Diclofenac Drug Interactions: What to Avoid and What to Tell Your Doctor

Diclofenac interacts with a wide range of medications, supplements, and substances. Some interactions are serious and require you to avoid the combination entirely. Others require dose adjustments or careful monitoring. Because Diclofenac is so commonly taken alongside other medications — especially by older adults managing multiple conditions — understanding these interactions is essential for your safety.

Major Interactions: Avoid or Use Only Under Close Medical Supervision

These interactions carry the highest risk of serious adverse events:

Warfarin (Coumadin) and other anticoagulants: Diclofenac increases the risk of bleeding when combined with blood thinners like warfarin. NSAIDs affect platelet function and can also damage the GI tract, creating a double bleeding risk. If you must use both, your INR (a measure of clotting time) must be monitored closely.

Other NSAIDs (ibuprofen, naproxen, aspirin): Do not take Diclofenac with any other NSAID. Combining NSAIDs adds toxicity with no additional pain benefit, significantly increasing GI bleeding, kidney, and cardiovascular risks. Check OTC products carefully — many cold, flu, and pain relievers contain ibuprofen or aspirin.

Ketorolac (Toradol): The combination of Diclofenac and ketorolac is contraindicated — both increase toxicity of the other through pharmacodynamic synergism. Avoid this combination entirely.

Methotrexate: NSAIDs can reduce the renal elimination of methotrexate, potentially increasing methotrexate toxicity. Use with caution; your doctor may need to reduce methotrexate dose or monitor levels closely.

Moderate Interactions: Use With Caution and Monitoring

ACE inhibitors and ARBs (lisinopril, enalapril, losartan, valsartan): Diclofenac can reduce the blood pressure-lowering effect of these medications and increase the risk of kidney injury when used together. If you take a blood pressure medication, your doctor should monitor your kidney function and blood pressure.

Diuretics (furosemide, hydrochlorothiazide): NSAIDs can reduce the effectiveness of diuretics ("water pills") and increase the risk of kidney problems. This combination requires caution, particularly in elderly patients and those with heart failure.

Lithium: NSAIDs can reduce lithium elimination from the kidneys, leading to higher lithium blood levels and risk of lithium toxicity. If you take lithium for bipolar disorder, your doctor will need to monitor lithium levels.

Corticosteroids (prednisone, dexamethasone): Combining Diclofenac with steroids significantly increases GI bleeding risk. Use the lowest possible doses of both and consider co-prescribing a proton pump inhibitor (PPI) for stomach protection.

SSRIs and SNRIs (sertraline, fluoxetine, venlafaxine, duloxetine): Antidepressants that affect serotonin levels can increase GI bleeding risk when combined with NSAIDs. If you take an SSRI or SNRI with Diclofenac, ask your doctor about co-prescribing a stomach protectant.

Antiplatelet drugs (clopidogrel/Plavix, aspirin for heart protection): Both NSAIDs and antiplatelet drugs affect the blood's ability to clot. Combined use increases bleeding risk. Note: if you take low-dose aspirin (81 mg) for heart protection and need an NSAID, talk to your cardiologist first.

Food and Supplement Interactions

Alcohol: Alcohol combined with Diclofenac significantly increases GI bleeding risk and liver strain. Avoid alcohol while taking Diclofenac, especially with regular use.

Fish oil and omega-3 supplements: High-dose fish oil has mild antiplatelet effects. Combined with Diclofenac, this could theoretically increase bleeding risk. Mention any supplements to your doctor.

Ginkgo biloba: This herbal supplement has antiplatelet properties and may increase bleeding risk when combined with NSAIDs.

What to Tell Your Doctor Before Starting Diclofenac

Always give your doctor and pharmacist a complete medication list before starting Diclofenac. Be sure to mention:

All prescription medications, especially blood thinners, blood pressure medications, steroids, antidepressants, lithium, and methotrexate

All OTC medications, especially ibuprofen (Advil), naproxen (Aleve), or aspirin

Vitamins, supplements, and herbal products (especially fish oil, ginkgo, garlic supplements)

Alcohol consumption habits

For a full review of Diclofenac's side effects and safety profile, see our comprehensive Diclofenac side effects guide.