Effect of 0.5 mg versus 1 mg varenicline for smoking cessation: a randomized controlled trial

Aims Varenicline is used in smoking cessation. The aims of the trial were to test for differences between standard 1- and 0.5-mg doses (both twice daily during 8 weeks) in (1) abstinence, (2) adherence and (3) side effects. Design Open-label randomized parallel-group controlled trial with 1-year follow-up. All those randomized were included in the final sample using an intention-to-treat (ITT) approach. Setting Stop-Smoking Clinic of the Virgen Macarena University Hospital in Seville, Spain. Participants The study comprised smokers (n = 484), 59.5% of whom were men with a mean age of 50.67 years and a smoking history of 37.5 pack-years. Intervention and comparator Participants were randomized to 1 mg (n = 245) versus 0.5 mg (n = 239) and received behavioural support, which consisted of a baseline visit and six follow-ups during 1 year. Measurements The primary outcome was continuous self-reported abstinence during 1 year, with biochemical verification. The secondary outcomes were adherence and side effects. Also measured were baseline demographics, medical history and smoking characteristics. Findings Abstinence rates at 1 year were 46.5% with 1 mg versus 46.4% with 0.5 mg [odds ratio (OR) = 0.997; 95% confidence interval (CI) = 0.7-1.43; P = 1.0]; Bayes factor in favour of H0 = 238.507, Bayes factor against H0 = 0.004. Treatment adherence was similar in both regimens (OR = 1.16; 95% CI = 0.8-1.7; P = 0.44). Side effects were reported in 19.3% of cases with 1 mg versus 12.1% with 0.5 mg, although with no significant differences between regimens (OR = 1.73; 95% CI = 0.94-3.18; P = 0.093). Conclusions There appears to be no difference in smoking cessation effectiveness between 1mg and 0.5mg varenicline, both administered twice daily for 8 weeks, with similar rates of abstinence (46.5% versus 46.4%), adherence and side effects.