Cimetidine is used to reduce the pain of ulcer and heartburn or to assist in the healing of ulcers and damage caused by gastroesophageal reflux disease (GERD).

Cimetidine is used to prevent ulcers in certain circumstances and to treat certain conditions that are associated with over secretion of acid by the stomach (i.e., Zollinger-Ellison Syndrome, systemic mastocytosis, and multiple endocrine adenomas). It has also been used to manage digestive tract symptoms of cystic fibrosis in adolescents. The medication works by reducing the amount of acid secreted by the stomach.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended adult dose of cimetidine depends on the condition being treated.

When treating duodenal or gastric ulcers, the dose ranges from 800 mg to 1,200 mg daily, in divided doses. It is usually taken for 4 to 6 weeks, to ensure that the ulcer has healed.

To prevent recurrent ulcers, the dose ranges from 400 mg to 600 mg. If prevention is needed, this dose should be continued for 6 to 12 months.

The recommended dose of cimetidine to treat ulcers caused by anti-inflammatory medications is 800 mg daily, either as 400 mg taken twice a day or 800 mg taken at bedtime. If the anti-inflammatory is not stopped, the cimetidine may be continued as 400 mg at bedtime.

To treat gastroesophageal reflux disease (GERD), the recommended dose is 1,200 mg daily in divided doses.

To reduce the amount of stomach acid produced in conditions that cause over secretion, the dose should be started at 300 mg taken 4 times a day, but may be increased to control symptoms to a maximum of 2,400 mg daily.

Many things can affect the dose of a medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

Cimetidine can be taken with or without food.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take this medication if you are allergic to cimetidine or any ingredients of the medication.

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 this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. 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 ability (especially for people with Zollinger-Ellison syndrome who have been taking high doses of cimetidine for at least one year)
• diarrhea
• 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
• difficulty passing urine
• dizziness
• fast, pounding, or irregular heartbeat
• fever
• hallucinations (seeing or hearing things that aren't there)
• joint and pain stiffness
• mood or mental changes (e.g., anxiety, agitation, confusion, hallucinations, depression, nervousness, or severe mental illness)
• muscle cramps or aches
• 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)
• symptoms of kidney inflammation (e.g., nausea, vomiting, decreased appetite, difficulty breathing, fatigue, increased frequency of urination)
• symptoms of muscle inflammation (e.g., weakness, difficulty rising from sitting, trouble reaching overhead)

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)

• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, fever, chills, rapid heartbeat, swollen abdomen)
• symptoms of irregular heartbeat (e.g., chest pain, dizziness, rapid or pounding heartbeat, shortness of breath)

• 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 this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Kidney function: People with kidney disease are at risk for increased side effects. People with kidney disease or reduced kidney function should discuss with their doctor how this medication may affect their medical condition, how their medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Stomach cancer: Using medications such as cimetidine may prevent symptoms of stomach cancer from being noticed. If you have recurrent vomiting, difficulty swallowing, blood in the stool, significant unintentional weight loss, fatigue (anemia), or are coughing up blood, check with your doctor right away. If you have heartburn that worsens or returns after using this medication continuously for 2 weeks, check with your doctor.

Pregnancy: The safety of this medication for use during pregnancy has not been established. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication passes into breast milk. If you are breast-feeding and taking cimetidine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children and adolescents younger than 16 years of age.

Seniors: Seniors may be more at risk of side effects such as confusion and dizziness. They may also be more likely to experience interactions with other medications when taking cimetidine.

There may be an interaction between cimetidine and any of the following:

• amiodarone
• atorvastatin
• azelastine
• azole antifungal medications (e.g., itraconazole, ketoconazole)
• benzodiazepines (alprazolam, bromazepam, and triazolam)
• calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
• carbamazepine
• capecitabine
• cefuroxime
• clobazam
• clozapine
• cyclosporine
• erythromycin
• finerenone
• flibanserin
• gliclazide
• HIV protease inhibitors (e.g., atazanavir, fosamprenavir)
• hydroxychloroquine
• ledipasvir
• lemborexant
• lidocaine
• lomitapide
• melatonin
• metformin
• mirtazapine
• moclobemide
• multiple vitamin/mineral supplements
• octreotide
• pentoxifylline
• phenytoin
• praziquantel
• pramipexole
• procainamide
• propranolol
• protein kinase inhibitors (e.g., acalabrutinib, bosutinib, dacomitinib, erlotinib, nilotinib, selpercatinib)
• rilpivirine
• risedronate
• roflumilast
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, escitalopram, fluoxetine, sertraline)
• simvastatin
• sirolimus
• tacrolimus
• tamsulosin
• theophyllines (e.g., aminophylline, theophylline)
• tizanidine
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, imipramine)
• velpatasvir
• warfarin
• zolmitriptan

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.