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If you also take ketoconazole (Nizoral), take it at least 2 hours before you take cimetidine.

Before taking this medication, tell your doctor if you are using any of the following medicines:

• a blood thinner (warfarin or Coumadin);

• phenytoin (Dilantin);

• nifedipine (Adalat);

• metronidazole (Flagyl);

• propranolol (Inderal);

• chlordiazepoxide (Librium);

• lidocaine (Xylocaine);

• diazepam (Valium);

• theophylline (Theo-Dur, Slo-Bid, Bronkodyl); or

• depression or anxiety medication such as amitriptyline (Elavil), imipramine (Tofranil), clomipramine (Anafranil), desipramine (Norpramin), nortripytyline (Aventyl).

You may not be able to take cimetidine, or you may require a dosage adjustment or special monitoring during treatment if you are taking any of the medicines listed above.

There may be other drugs not listed that can affect cimetidine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Stop using cimetidine and get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have any of these serious side effects:

• cough, fever, chest congestion, trouble breathing;

• red or blistering skin rash;

• jaundice (yellowing of the skin or eyes);

• easy bruising or bleeding, unusual weakness;

• feeling faint, light-headed, disoriented, or confused;

• urinating less than usual;

• irregular heartbeat; or

• a rash.

Other less serious side effects are more likely to occur. Talk with your doctor if you have any of these side effects:

• feeling dizzy, depressed, or agitated;

• breast swelling or tenderness (in men);

• joint or muscle pain;

• mild skin rash;

• headache; or

• diarrhea, nausea, or constipation.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.