See also How to Use section.
Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.
This drug should not be used with the following medications because very serious interactions may occur: cisapride, dofetilide, epirubicin.
If you are currently using any of these medications listed above, tell your doctor or pharmacist before starting cimetidine.
Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially of: artemether, clopidogrel, carmustine, lumefantrine, metformin, moclobemide, moricizine, procainamide, quinidine, silver sulfadiazine, drugs removed from your body by certain liver enzymes (such as lidocaine, metoprolol, propranolol, tacrine, warfarin, zaleplon, anti-seizure drugs including carbamazepine and phenytoin, benzodiazepines including diazepam, calcium channel blockers including diltiazem, narcotic analgesics including codeine, tricyclic antidepressants including amitriptyline, theophylline and related drugs).
Since cimetidine reduces the amount of acid in your stomach, it may also change the absorption of certain medications and affect how they work. Some examples of affected drugs include atazanavir, dasatinib, delavirdine, certain azole antifungals (such as itraconazole, ketoconazole), among others. Ask your doctor or pharmacist if any of the medications you take are affected by cimetidine and how to manage this interaction.
Check the labels on all your medicines because they may contain nonsteroidal anti-inflammatory drugs (NSAIDs such as aspirin, ibuprofen, naproxen) that may cause stomach irritation/ulcers. Ask your pharmacist about the safe use of those products. Low-dose aspirin should be continued if prescribed by your doctor for specific medical reasons such as heart attack or stroke prevention (usually at dosages of 81-325 milligrams per day). Consult your doctor or pharmacist for more details.
Cigarette smoking can affect this medication. Tell your doctor if you smoke and if you stop or start smoking while using this medication.
This medication and similar H2 blockers (e.g., famotidine, nizatidine, ranitidine) are available both with and without a prescription. Do not take them at the same time.