Study characteristics
As shown in Table 1, the included RCTs involved 1565 alcohol-drinking smokers (803 in treatment groups and 762 in control groups). All studies were published between 2005 and 2020 in the United States (n = 13), United Kingdom (n = 1) and Canada (n = 1). Most smokers were over 40 years of age and smoked more than ten cigarettes per day. All studies were the two-arm design and the treatment group in each RCT examined one of six drugs, including Varenicline (n = 5), Naltrexone (n = 4), Topiramate (n = 2), Bupropion (n = 3), and Baclofen (n = 1), meanwhile all RCTs gave a placebo to the control group. The duration of the measurement phase ranged from four weeks to 52 weeks, and the smoking cessation rate was the outcome indicator of all studies, including 7-day point prevalence abstinence, prolonged (continuous) abstinence, and other point prevalence abstinence (direct reports at each stage).