This is a prospective double-blind randomized placebo-controlled trial. A total of 450 dyspeptic adult patients, who are diagnosed with functional dyspepsia in accordance with Rome III criteria, are randomly allocated in a 1:1 proportion to receive either lansoprazole 15mg or placebo once daily for 8 weeks. Primary outcome is complete relief of dyspeptic symptoms. Secondary outcomes include significant symptomatic relief, improvement of dyspepsia severity, and health-related quality of life. We use a multiple logistic regression analysis to investigate whether dyspepsia subgroups are associated with different therapeutic responses.