BACKGROUND. Data on smoking cessation and relapse for 6 yers of the Multiple Risk Factor Intervention Trial were evaluated in univariate and multivariate analyses to determine the relationship between variables measured at the beginning of the trial and smoking cessation and relapse for special intervention and usual care participants. RESULTS. The variables positively associated with smoking cessation in both the SI and the UC groups included age, education, and past success in quitting; there was a negative association with the number of cigarettes smoked per day. The expectation of quitting was positively associated with cessation in the special intervention group only, while life events, alcohol, and the presence of a wife who smokes were significant predictors of reduced cessation for the usual care group. The special intervention program may have overcome obstacles which interfered with cessation among the usual care participants. Associations with relapse were generally stronger in the usual care group than in the special intervention group. For usual care participants, multivariate analyses showed that education, past success in quitting smoking, alcohol, and life events were associated with relapse rates. For special intervention participants, only alcohol emerged as a significant predictor. CONCLUSION. The data are relevant in terms of factors that govern smoking cessation and relapse for adult smokers who take part in formal intervention programs and for those who are left to modify their behavior on their own.

The Multiple Risk Factor Intervention Trial (MRFIT) is a 6-year clinical trial for the study of the prevention of heart disease. Twelve thousand eight hundred and sixty-six men in the upper 10–15% of heart attack risk were randomly assigned to Special Intervention (SI) or Usual Care (UC). The SI participants received “risk factor” (hypertension, hypercholesterolemia, and cigarette smoking) intervention at the clinical centers; the UC participants were referred to their usual source of medical care for treatment. Forty percent of SI and 21% of UC smokers at entry reported not smoking at year 4, with lighter smokers in both treatment groups reporting significantly more cessation than heavier smokers. The greatest SI-UC difference in cessation rate was achieved during the first year of the program. The use of serum thiocyanate, an objective indicator of cigarette smoking, avoided problems inherent in self-reported data. Misreporting of smoking status was found in both groups with more occurring among the SI smokers. Cohort analysis revealed that of the smokers who stopped during the first year of the trial, 68% of SI and 57% of UC remained abstinent through the 4-year follow-up. Of the smokers who stopped later in the program the UC had better maintenance rates than the SI.