These two drugs are H2-receptor antagonists and are used in acid reflux treatment. When first introduced cimetidine and later ranitidine were used so extensively, the potential side effects were reported early.

The general conclusion is that this group is relatively safe and unwanted side effects are rare and reversible on withdrawal of the drug.

The commonest reported side effects are diarrhoea, muscle pains, transient rashes, and dizziness. Cimetidine has more side effects than ranitidine. Cimetidine has been reported to cause gynaecomastia (enlarged breast) in men. This is very rare and due to stimulation of androgen receptors.

Cimetidine, by inhibiting cytochrome P450, can slow down metabolism of certain drugs. By doing this the effects of these drugs are potentiated. The drugs in this group are anti-coagulants, theophylline, phenytoin, tri-cyclic anti-depressants and carbamazepine.

Cimetidine can also cause confusion in the elderly.

Ranitidine has a much lower effect on androgen reception and less likely to cause gynaecomastia. It also has mush less effect on cytochrome P450, and therefore, not likely to enhance the effects of the drugs mentioned above.

As side effects in this group are very rare, this makes cimetidine and ranitidine excellent acid reflux treatment.

Dr. Phil Hariram,