Study characteristics
As shown in Table 1, the included RCTs involved 908 smokers with alcohol dependence (450 in treatment groups and 458 in control groups). All studies were published between 2005 and 2020 in the United States (n = 8) and Canada (n = 1). Most smokers were over 40 years old and smoked more than ten cigarettes per day. The treatment group in each RCT examined one of four drugs, including Varenicline (n = 3), Naltrexone (n = 3), Topiramate (n = 2), Bupropion (n = 1), and all RCTs gave a placebo to the control group. The duration of the measurement phase ranged from two weeks to six months, and the outcome indicator of all studies was the smoking cessation rate