Cimetidine reduces the amount of acid produced in the stomach.
Any side-effects are usually mild and do not last long. The most common ones are diarrhoea, headache, dizziness and tiredness.
|Type of medicine||H2-receptor antagonist|
|Used for||Treatment of conditions caused by too much acid being produced in the stomach.|
|Available as||Tablets and oral liquid medicine|
Cimetidine belongs to a group of medicines that reduce the amount of acid produced by the cells in the lining of the stomach. They are called 'histamine H2-receptor antagonists', but are commonly also called H2 blockers.
Cimetidine is helpful in the treatment of conditions caused by too much acid being produced in the stomach. These conditions include stomach ulcers (gastric ulcers), ulcers of the upper part of the intestine (duodenal ulcers), acid reflux or heartburn (reflux oesophagitis), and indigestion. It can also be used to treat stomach irritation and/or ulceration caused by non-steroidal anti-inflammatory drugs (NSAIDs).
Acid is produced naturally in your stomach to help to digest food. Excessive amounts of acid can irritate the lining of your stomach, causing inflammation, ulcers and other conditions. Cimetidine works by reducing the amount of acid produced by your stomach. This helps to relieve symptoms and assist the healing process where damage has already occurred.
Before taking cimetidine
To make sure this is the right treatment for you, before you start taking cimetidine it is important that your doctor or pharmacist knows:
- If you are pregnant, trying for a baby or breast-feeding.
- If you have any of the following symptoms: difficulty swallowing, loss of blood, weight loss, or if you are being sick (vomiting).
- If you have any problems with the way your liver works, or with the way your kidneys work.
- If you have ever had an allergic reaction to a medicine.
- If you are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.
How to take cimetidine
- Before you start this treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about cimetidine and will provide you with a full list of the side-effects which you may experience from taking it.
- Take cimetidine exactly as your doctor tells you to. There are different strengths of tablets available - 200 mg, 400 mg, and 800 mg. You may be prescribed the tablets to take once, twice, or four times a day. Your doctor will tell you what dose is right for you and the directions will also be on the label of the pack to remind you what was said.
- You can take cimetidine before or after meals.
- If you forget to take a dose at your usual time, you can take it when you remember (unless it is nearly time for your next dose, in which case leave out the missed dose). Do not take two doses together to make up for a forgotten dose.
Getting the most from your treatment
- A course of treatment can vary in length, depending upon the reason why you are taking cimetidine. It may be just for a few days to relieve your symptoms, or for several weeks to help an ulcer heal. Keep any appointments that you have booked with your doctor so that your progress can be checked.
- Some foods may make your symptoms worse. Foods and drinks that have been suspected of this include peppermint, tomatoes, chocolate, spicy foods, hot drinks, coffee, and alcoholic drinks. If it seems that a food is aggravating your symptoms, try avoiding it for a while to see if your symptoms improve. Also, try avoiding eating large meals, as these can make your symptoms worse too.
- If you are overweight, it puts extra pressure on your stomach and encourages the symptoms of acid reflux. Losing some weight and eating a healthy balanced diet may help you.
- Smoking increases the amount of acid produced by the stomach and may make your symptoms worse. If you are a smoker, speak with your doctor or pharmacist about how to quit.
- If you buy any medicines 'over the counter', always check with a pharmacist that they are safe to take alongside your other medicines. Cimetidine can interfere with the way other medicines work.
Can cimetidine cause problems?
Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains some of the most common ones associated with cimetidine. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any of the following continue or become troublesome.
|Common cimetidine side-effects (these affect fewer than 1 in 10 people)||What can I do if I experience this?|
|Diarrhoea||Drink plenty of water to replace lost fluids|
|Headache, muscle aches||Drink plenty of water and ask your pharmacist to recommend a suitable painkiller. If the aches continue, let your doctor know.|
|Feeling dizzy or tired||Do not drive and do not use tools or machines until you feel well again|
|Skin rash||If troublesome, speak with your doctor|
If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.
How to store cimetidine
- Keep all medicines out of the reach and sight of children.
- Store in a cool, dry place, away from direct heat and light.
Important information about all medicines
Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital. Take the container with you, even if it is empty.
This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
If you are having an operation or any dental treatment, tell the person carrying out the treatment which medicines you are taking.
Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
If you have any questions about this medicine ask your pharmacist.
Further reading and references
Manufacturer's PIL, Cimetidine 200 mg/5 ml Oral Solution; Rosemont Pharmaceuticals Ltd, The electronic Medicines Compendium. Dated September 2018.
Manufacturer's PIL, Cimetidine Tablets 200 mg, 400 mg, 800 mg; Accord Healthcare Ltd, The electronic Medicines Compendium. Dated February 2019.
British National Formulary, 79th Edition (Mar 2020); British Medical Association and Royal Pharmaceutical Society of Great Britain, London.