Oral contraceptive use and smoking are risk factors for relapse in Crohn's disease. The Canadian Mesalamine for Remission of Crohn's Disease Study Group.

Background & Aims: Lifestyle factors have been shown to influence prognosis in Crohn's disease. The purpose of this study was to prospectively assess the effects of smoking and oral contraceptive use on clinical relapse rates.

Methods: Placebo-treated patients formed a prospective cohort, followed up for 48 weeks or until relapse. The influence of smoking and the use of oral contraceptives on relapse risk was examined by life-table analysis (log rank tests) and Cox proportional hazards modeling, taking into account demographic and disease characteristics.

Results: Of 152 patients, 61 (40%) had a relapse. Univariate analysis showed unfavorable outcomes for women (P = 0.05), current smokers (P = 0.005), and use of oral contraceptives (P = 0.001). Recent surgery was associated with a decreased risk of relapse (P = 0.02). The Cox model retained current smoking vs. never smoking (hazard ratio, 2.1; 95% confidence interval, 1.1-4.2), oral contraceptive use (hazard ratio, 3.0; 95% confidence interval, 1.5-5.9), and medical compared with surgical induction of remission (hazard ratio, 2.1; 95% confidence interval, 1.0-4.2) as predictors of relapse. Ex-smokers did not have an increased risk. Finally, sex, age, time in remission, disease location, and disease duration were not significant predictors.

Conclusions: Oral contraceptive use and smoking are associated with an increased risk of relapse in patients with Crohn's disease.