Both PPI and H2RA lead to increased circulating levels of gastrin,5–7 which has been associated with increased risk of colorectal cancer in prospective studies.11 In animal models of colorectal cancer, gastrin leads to increased proliferation of colon mucosa and adenoma progression.8–10 It is possible that the rise in gastrin levels due to PPI and H2RA use is not sufficient to promote development of colorectal tumours. This evidence concerns the gene GAST and adenoma.