Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes Cimetidine. If you are concerned about side effects, discuss the risks and benefits of Cimetidine with your doctor.

The following side effects have been reported by at least 1% of people taking Cimetidine. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• decreased sexual desire
• decreased sexual ability (especially for people with Zollinger-Ellison syndrome who have been taking high doses of cimetidine for at least one year)
• Diarrhea
• drowsiness
• headache
• loss of hair
• swelling of the breasts or breast soreness (women and men)
• tiredness

Although most of these side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• confusion
• dizziness
• fainting
• fast, pounding, or irregular heartbeat
• general feeling of discomfort or illness
• mood or mental changes (e.g., anxiety, agitation, confusion, hallucinations, Depression, nervousness, or severe mental illness)
• muscle cramps or aches
• red or irritated eyes
• signs of allergic reaction (e.g., Hives, skin rash, or itching)
• signs of Anemia (low red blood cells; e.g., dizziness, pale skin, unusual tiredness or weakness, shortness of breath)
• signs of bleeding (e.g., bloody nose, blood in urine, coughing blood, cuts that don't stop bleeding)
• signs of infection (e.g., coughing or difficulty swallowing, sore throat, Fever or chills, flu-like symptoms, swollen or painful glands)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of inflammation of blood vessels (e.g., fever, fatigue, weight loss, loss of appetite, headache, numbness or weakness, muscle or joint pain)
• symptoms of a severe skin rash (e.g., blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Cimetidine.