The morbidity and mortality rates attributed to smoking are substantial and cigarette smoke remains the first preventable cause of premature death worldwide. Despite the knowledge of the adverse consequences of smoking, many smokers struggle to quit. Cigarette smoking is the primary cause of chronic obstructive pulmonary disease, and smoking cessation represents the most effective way of stopping its progression. Varenicline is one of the first-line smoking cessation aids recommended in many Clinical Practice Guidelines and its efficacy and safety have been demonstrated in several clinical trials. Varenicline has a unique mechanism of action and clinical trials support its use as an effective and generally well-tolerated therapy. This article reviews the clinical pharmacological trials on smoking cessation published in recent years on varenicline, with particular attention to the outcomes used in the studies. MedLine, the Cochrane database and Embase were evaluated. Almost all the trials have, as a primary endpoint, the abstinence from cigarettes at 9-12 weeks of treatment. Only one study considers lung function spirometric changes as a secondary endpoint. No study has evaluated lung function. This marker could be very important as a way of evaluating, objectively, an improvement in lung function, which correlates also with subjective parameters, as dyspnea and fatigue.