BMA Concise Guide to Medicine & Drugs


Brand name Tagamet

Used in the following combined preparations None


Drug group Anti-ulcer drug

Overdose danger rating Low

Dependence rating Low

Prescription needed No (some preparations)

Available as generic Yes


Cimetidine reduces the secretion of gastric acid and pepsin (an enzyme that helps in the digestion of protein) and thereby promotes ulcer healing in the stomach and duodenum. It is also used for reflux oesophagitis, in which acid stomach contents may flow up the oesophagus. Treatment is usually given in four- to eight-week courses, with further short courses if symptoms recur. Cimetidine also affects the actions of certain enzymes in the liver. It is therefore prescribed with caution to people taking other drugs, particularly drugs whose levels need to be carefully controlled. Since cimetidine promotes healing of the stomach lining, it may mask the symptoms of stomach cancer and delay diagnosis. It is therefore prescribed with caution to patients whose symptoms change or persist, and in middle aged and older people.


Follow instructions on the label. Call your doctor if symptoms worsen.

How taken/used Tablets, liquid, injection.

Frequency and timing of doses 1–4 x daily (after meals and at bedtime).

Adult dosage range 800–1,600mg daily (occasionally increased to 2,400mg daily)

Onset of effect Within 90 minutes.

Duration of action 2–6 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children. Protect from light.

Missed dose Do not take the missed dose. Take your next dose as usual.

Stopping the drug If prescribed by your doctor, do not stop taking the drug without consulting him or her because symptoms may recur.

Exceeding the dose An occasional unintentional extra dose is unlikely to be a cause for concern. But if you notice any unusual symptoms, or if a large overdose has been taken, notify your doctor.


Adverse effects are uncommon with cimetidine. They are usually related to dosage level and almost always disappear when the drug is stopped. The adverse effects include diarrhoea, dizziness, tiredness, muscle or joint pain, and, in men, breast enlargement and erectile dysfunction (impotence). If any of these symptoms occur, seek medical advice. If the drug causes confusion or hallucinations, stop taking it and consult your doctor.


Benzodiazepines Cimetidine may increase the blood levels of some of these drugs, increasing the risk of adverse effects.

Theophylline/aminophylline Cimetidine may increase the blood levels of these drugs and their dose may need to be reduced.

Sildenafil Cimetidine may increase the blood level of this drug.

Beta blockers and antiarrhythmic drugs Cimetidine may increase the blood levels of these drugs.

Anticonvulsant drugs Cimetidine may increase the blood levels of these drugs, and their dose may need to be reduced.

Anticoagulant drugs Cimetidine may increase the effect of anticoagulants and their dose may need to be reduced.

Ciclosporin and tacrolimus Cimetidine may increase the blood levels of these drugs.


Be sure to consult your doctor or pharmacist before taking this drug if:

· You have long-term liver or kidney problems.

· You are taking other medicines.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding The drug passes into the breast milk, but at normal doses adverse effects on the baby are unlikely. Discuss with your doctor.

Infants and children Reduced dose necessary.

Over 60 Risk of stomach cancer is higher in the elderly and it must be excluded before cimetidine is prescribed. The drug is also more likely to cause confusion and depression in the elderly.

Driving and hazardous work Avoid such activities until you have learned how cimetidine affects you because the drug may cause dizziness and confusion.

Alcohol Avoid. Alcohol may aggravate the underlying condition and counter the beneficial effects of cimetidine.


Courses of longer than 8 weeks are not usually necessary.