Cimetidine side effects and drug information

Cimetidine is a treatment and a type of prevention for certain stomach ulcers, and it also reduces stomach acid. This drug is used as a treatment for certain conditions like gastroesophageal reflux disease, which happens when the acid in the stomach goes back up into the esophagus and results in heartburn.

CAS Number 51481-61-9
PubChem CID 2756
DrugBank DB00501
ChemSpider 2654


This medication alqo comes in a non- prescription version and is available as a treatment for heartburn that is caused by acid indigestion and sour stomach. Cimetidine is used as well as prevention for this condition. This drug may have other uses that are not found in the guide.

Important Information

Take Cimetidine exactly as prescribed and inform your doctor about all the other medicines you are taking, as well as your other medical issues, and if you have allergies.

Before taking Cimetidine

If you are experiencing chest pain that is spreading to your shoulder or jaw and is feeling light-headed or anxious, seek medical attention to be sure that you are only having heartburn and not a heart attack. If you have allergies to stomach acid reducers or to cimetidine itself, do not take this medication. If you have the following condition, consult with your doctor first if you can use this product:

  • Kidney or liver disease
  • Persistent chest pain
  • Long-lasting heartburn
  • Difficulty in swallowing
  • Sudden weight loss
  • Heartburn that comes with wheezing

If you are pregnant or breastfeeding, discuss with your doctor if you can take this drug. Never let a child take this medication without the doctor’s instructions.

How should I take Cimetidine?

Take Cimetidine as prescribed and have it with meals or during bedtime. To avoid heartburn, take this drug about half an hour prior to food or drink consumption.  This medication should be consumed with a glass of water, and the improvement of the condition is expected after around 8 weeks of treatment. Smoking may affect the time of healing, and if this does not improve the symptoms, see your doctor. Over- the- counter formulation of this drug must not be used for more than 14 days unless per doctor’s advice. Cimetidine should be protected from heat, light, and moisture and be kept at room temperature.

Side Effects

The use of this medication may cause some reaction. If any of these symptoms worsen or becomes persistent, see your doctor immediately:

  • Enlargement of the breast
  • Dizziness
  • Headache
  • Drowsiness
  • Diarrhea

Serious side effects are rare, but if they develop, consult your doctor right away. Some of these are:

  • Hallucinations
  • Depression
  • Nervousness
  • Excitability

Other side effects may arise aside from the ones mentioned. See your health care provider if you think you have uncommon symptoms while under this treatment.

Indication and Dosage

Usual Adult Dose for Duodenal Ulcer

For this type of condition, once daily should be taken at bedtime with the dosage from 800mg to 1600mg. Treatment for this should last a maximum of 6 weeks. Cimetidine is used as short- term treatment for active duodenal ulcer, and patients usually heal at around four weeks. Medication may be ceased earlier if the condition has improved.   This drug may be taken along with antacids as a treatment for pain (if necessary), but taking them together at the same time is not advised as it may interact with this medicine’s absorption.

Usual Adult Dose for Duodenal Ulcer Prophylaxis

For this condition, this drug should be taken once daily with 400mg dosage, and during bedtime. The length of treatment is up to a maximum of 5 years. When an active ulcer is healed, dosage may be reduced for maintenance treatment of duodenal ulcer.

Usual Adult Dose for Gastric Ulcer

For the treatment of gastric ulcer, Cimetidine should be taken once daily with 800mg dosage during bedtime; or four times per day if the dosage is at 300mg. If the latter, it should be taken with meals and the final dose during bedtime. The length of treatment for this condition is around eight weeks.   This medication is used for short- term treatment of active benign gastric ulcer. For lower risk of drug interaction, taking this drug once daily is usually preferred.

Usual Adult Dose for Zollinger- Ellison Syndrome

To treat Zollinger- Ellison Syndrome, this drug should be taken four times daily with 300mg dosage between meals, then the final dose during bedtime.   A maximum of 2,400 mg per day should only be consumed, and patients usually experience improvement or healing after four weeks of treatment. Cimetidine is used as a treatment for pathological hypersecretory conditions.

Usual Adult Dose for Erosive Esophagitis and Usual Adult Dose for Gastroesophageal Reflux Disease

For these conditions, Cimetidine should be taken four times daily with 400mg dosage or twice a day with 800mg dosage. The length of treatment for these conditions is around 12 weeks, and this medication is used to treat lesions as well as manage the symptoms. It is also used to treat erosive esophagitis and erosive gastroesophageal reflux disease.

Usual Adult Dose for Dyspepsia

For over- the- counter formulations: To relieve symptoms, take 200 mg by mouth along with a glass of water. To prevent symptoms, take 200mg within 30 minutes prior to food and/ or drink consumption. The maximum dosage is only two tablets, and the length of self- treatment is a maximum of 14 days. This medicine is used to provide relief for heartburn caused by acid indigestion and sour stomach. Usual Pediatric Dose for Duodenal Ulcer/ Usual Pediatric Dose for Duodenal Ulcer Prophylaxis. Usual Pediatric Dose for Erosive Esophagitis. Usual Pediatric Dose for Gastric Ulcer. Usual Pediatric Dose for Gastroesophageal Reflux Disease. Usual Pediatric Dose for Stress Ulcer Prophylaxis. Usual Pediatric Dose for Zollinger- Ellison Syndrome For these types of conditions in children, Cimetidine should only be used if necessary. And if they should take it, about only 20 to 40 mg per kg once daily should be consumed. This medication is used to treat short- term active duodenal ulcer, and when this condition is healed, the dosage is reduced as maintenance for duodenal ulcer. Cimetidine is also used as short- term treatment for active benign gastric ulcer as well as used to prevent upper gastrointestinal bleeding in seriously ill patients.   This drug is also used to treat pathological hypersecretory conditions, erosive esophagitis, and erosive GERD.

Usual Pediatric Dose for Dyspepsia

For over- the- counter formulations, the recommended dosage for 12 years old and up are the following: To provide relief for symptoms, take 200 mg of the medicine To prevent symptoms, take 200 mg within 30 minutes prior to the consumption of food and/ or drink. The maximum dosage for children should only be two tablets daily, and the length of self- treatment is 14 days. Cimetidine OTC formulation is used to provide relief for heartburn caused by acid indigestion and sour stomach.

Renal Dose Adjustments

For renal dysfunction that is severe, take 300mg with 12-hour intervals, and may be increased to an 8-hour interval depending on the individual’s condition. For renal failure that is severe, the lowest time of distribution for dosing should be appropriate to how the patient would respond to the medication.

Drug Interaction

Make sure that you have informed your doctor about all your other medications before starting with this product as it is known to cause interactions with other drugs such as:

  • Terfenadine
  • Lomitapide
  • Astemizole
  • Pimozide
  • Cisapride
  • Eliglustat
  • Dofetilide

This medication has about 143 serious interactions with certain drugs, 193 moderate interactions with different medicines, and about 69 mild drug interactions.

Warnings and Precautions

Concerns associated with adverse effects:

  • Confusion
  • Deficiency in Vitamin B12

Concerns related to diseases:

  • Renal impairment
  • Gastric malignancy
  • Hepatic impairment

Cimetidine may also interact with several other drugs, and great caution must be used for older people as there are potential risks such as having effects on their central nervous system or may cause confusion.

Overdose and Contraindications

Extreme sensitivity to this drug or any of its ingredients. If you are taking over- the- counter formulation for self- treatment, avoid using Cimetidine if you are experiencing the following conditions: difficulty in swallowing food, excreting black or bloody stools, vomiting with blood, is allergic to any of the drug’s component or to Cimetidine itself, or any other acid reducers. This drug is not intended to be used with other acid reducers. There is not enough study on the allergenic cross-sensitivity for histamine H2 antagonists. Still, due to the familiarity of the chemical structure and the pharmacologic reactions, the chance of cross-sensitivity cannot be denied.

Clinical Pharmacology

Pharmacokinetics Category Histamine H2 Antagonist Toxicology Aggressive restraint of histamine at H2 receptors of the gastric parietal cells that lead to a reduction in the secretion of the gastric acid, concentration of hydrogen ion, and gastric volume. Absorption Fast Metabolism Semi hepatic develops metabolites Excretion Mainly urine around 48%, and 2% feces Onset of Action 60 minutes Time to Peak 0.75 to 1 ½ hour

Medication Guide

Cimetidine is used as a treatment for:

  • Gastrointestinal ulcers
  • GERD
  • Sour stomach and heartburn
  • Other conditions that result from stomach acid

If you have any of these symptoms, see your doctor:

  • Hallucination
  • Confusion
  • Irritability
  • Liver problems
  • Changes in mood