OBJECTIVES: Acid-related diseases of the gastrointestinal system affect an estimated 29% of Canadian adults. Two drug classes, proton pump inhibitors (PPIs) and histamine–2 receptor antagonists (H2RAs) are commonly used to prevent and treat these conditions. PPIs have shown improved efficacy over H2RAs, and are generally considered to be safe medications with few adverse effects. However, there have been increasing concerns regarding adverse effects associated with long-term and high-dose PPI use. METHODS: Claims level data from the National Prescription Drug Utilization Information System (NPDUIS) Database were analyzed for seniors on public drug programs in 6 Canadian provinces between 2001-2002 and 2006-2007. This analysis compares PPI use to that of H2RAs and breaks down use by age and sex. The analysis also explores the influence PPI dosages and length of therapy may be having on the overall trend in PPI use. RESULTS: The age–sex standardized rate of PPI use among seniors on public drug programs increased from 13.1% in 2001–2002, to 21.1% in 2007–2008. During the same time period, H2RA use fell from 12.7% to 8.8%. The average daily dose of PPIs used by seniors on public drug programs remained relatively stable, with roughly 80% of PPI claimants using an average daily dose within the standard dosage range each year. The rate of chronic PPI use increased, with 65.8% of seniors taking PPIs considered to be chronic users in 2007-2008. CONCLUSIONS: There was a significant increase in the use of PPIs among seniors on public drug programs in Canada, which coincided with a decrease in H2RA use. Although the average daily dose of PPIs used by these seniors did not increase during the study period, a higher proportion of seniors were taking PPIs for longer periods of time.