Metformin is a widely used treatment for type 2 diabetes mellitus, but previous research suggests it also prevents colorectal cancer. Researchers conducted a double-blind, placebo-controlled multicentre trial in 151 patients without diabetes mellitus who had previously undergone removal of one or more colorectal adenomas or polyps. Patients treated with low-dose metformin for 1 year were found to have fewer ademomas or polyps than controls, with no severe adverse effects observed. Larger and more long-term trials are now required.