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

Background Low-dose aspirin is a risk factor for peptic ulcer disease but previous, population-based cohort studies may have underestimated the low-dose aspirin risk because they did not use a new-user design. Gastrointestinal bleeding occurs more frequently early after initiation of low-dose aspirin therapy than in later years. Aim To assess the associations of low-dose aspirin with gastric and duodenal ulcer incidence in prevalent- and new-user design. Methods Multivariate Cox regression models in the German ESTHER study (N = 7737) and the UK Biobank (N = 213,598) with more than 10 years of follow-up. Results In the prevalent-user design, there was no significant association between low-dose aspirin and gastric ulcer observed in both cohorts. Furthermore, low-dose aspirin was weakly, statistically significantly associated with prevalent duodenal ulcer in the UK Biobank (hazard ratio [95% confidence interval]: 1.27 [1.07-1.51]) but not in the ESTHER study (1.33 [0.54-3.29]). When restricting the exposure to only new users, the hazard ratios for incident gastric and duodenal ulcer disease were 1.82 [1.58-2.11] and 1.66 [1.36-2.04] in the UK Biobank, respectively, and 2.83 [1.40-5.71] and 3.89 [1.46-10.42] in the ESTHER study, respectively. Conclusions 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.