DRUG INTERACTIONS: This drug should not be used with the following medications because very serious interactions may occur: atazanavir, pemetrexed. If you are currently using any of these medications, tell your doctor or pharmacist before starting lansoprazole and naproxen. Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: alendronate, other medications for arthritis (e.g., aspirin, methotrexate), "blood thinners" (e.g., warfarin), cilostazol, corticosteroids (e.g., prednisone), cyclosporine, high blood pressure drugs (including ACE inhibitors such as captopril, angiotensin II receptor antagonists such as losartan, and beta-blockers such as metoprolol), lithium, other NSAIDs (e.g., ibuprofen, celecoxib), probenecid, theophylline, voriconazole, "water pills" (diuretics such as furosemide, hydrochlorothiazide, triamterene). Lansoprazole can decrease the effectiveness of certain drugs which require stomach acid in order to be absorbed. Before using this medication, consult your doctor or pharmacist on how to manage such a potential interaction if you are taking the following drugs: ampicillin, azole antifungals (e.g., ketoconazole, itraconazole), iron supplements. Based on information for similar drugs, lansoprazole may increase the amount of digoxin that is absorbed into your blood. Consult your doctor or pharmacist for details if you also take digoxin. This product can affect the results of certain lab tests. Make sure laboratory personnel and your doctors know you use this drug. Check all prescription and nonprescription medicine labels carefully since many contain pain relievers/fever reducers (NSAIDs such as aspirin or ibuprofen) which are similar to this drug. Aspirin, as prescribed by your doctor for reasons such as heart attack or stroke prevention (usually these dosages are 81-325 mg per day), should be continued. Consult your doctor or pharmacist for more details. Do not start or stop any medicine without doctor or pharmacist approval.