Smoking among oral contraceptive users in Quebec in 1987.

To determine whether an association exists between oral contraceptive (OC) use and cigarette smoking, the data base of the 1987 Québec Health Survey, a cross-sectional study of a provincial population, was sampled to provide a self-weighted subsample. This study population consisted of 292 OC users and a comparison group of 294 non-users, who would have been eligible to use OCs by virtue of their lacking contraindications to their use. 50.5% (95% CI: 44.8%-56.2%) of OC users smoked, as opposed to 41.0% (95% CI: 35.3%-46.7%) of non-users. There was a significant association between OC use and smoking; crude OR = 1.47, 95% CI: 1.06-2.04, p = 0.02. Controlling for effect modifiers and confounders by logistic regression revealed that the positive association prevails mainly in younger married, separated, and single women, whereas in women over 30 and cohabiting women the association is negative. While the negative association in women over 30 may reflect the efforts of physicians to prevent the adverse interactions between OC use and smoking by preventing older smokers from using OCs, the positive association in younger women indicates that physicians may be unable to prevent younger OC users from smoking.