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 1 mg and 0.5 mg varenicline, both administered twice daily for 8 weeks, with similar rates of abstinence (46.5% versus 46.4%), adherence and side effects.