During the past 2 decades, great advances have been made in the treatment of ulcer disease. This has involved the development of new drugs that are not only well tolerated, but are relatively inexpensive. The lack of significant adverse effects has revealed a degree of tolerability that, to write a review of the adverse effects, poses a difficult task. Most of the adverse effects are related to an excessive reaction to the relevant pharmacological characteristic that mediates the therapeutic response. The drug dosage can be reduced, freeing the patient of the adverse reaction, but leaving behind a background activity adequate to produce a therapeutically beneficial effect. The adverse effects of H2-antagonists fall into 2 groups. Firstly, there are poorly defined symptoms that have a prevalence similar to that in the community; these include headache, giddiness, dizziness, fatigue, constipation and diarrhoea. Secondly, they may delay the metabolism of drugs metabolised by the the cytochrome P450 system, and rarely be androgenic. Many antacids and the site-protective agent sucralfate contain aluminium, which can be absorbed, producing elevation of serum aluminium levels. In view of the possible association of aluminium with Alzheimer's disease, anxiety has arisen as to whether aluminium from these sources may, in those on prolonged treatment, cause Alzheimer's disease. However, the evidence so far indicates that aluminium is not a risk factor for Alzheimer's disease. The association of gastric cancer with achlorhydria has led to the fear that long term use of potent acid inhibitors may cause cancer. This fear has been accentuated by the observation that some rats, given omeprazole over their lifetime, developed carcinoid tumours of the stomach. However, enthusiastic research, both clinical and epidemiological, indicates that drug-induced achlorhydria is unlikely to be a problem in humans. Site protective agents have a role in certain conditions such as pregnancy where the systemic effect of a drug may produce adverse effects.
