Strongly increased risk of gastric and duodenal ulcers among new users of low-dose aspirin: results from two large cohorts with new-user design.

This study shows that low-dose aspirin is an independent risk factor for both gastric and duodenal ulcers. The associations were not significant or weak in the prevalent-user design and strong and statistically significant in the new-user design in both cohorts. Thus, it is important to weigh risks against benefits when low-dose aspirin treatment shall be initiated and to monitor adverse gastrointestinal symptoms after the start of low-dose aspirin therapy.