Tests of addiction treatments seldom reveal where treatment exercises its effect (i.e., promoting initial abstinence, preventing lapses, and/or impeding progression from lapse to relapse). The authors illustrate analyses distinguishing effects on these milestones in a randomized trial of high-dose nicotine patch (35 mg; n = 188) versus placebo (n = 136) in adult smokers, who used electronic diaries to monitor smoking in real time during 5 weeks of treatment. High-dose patch promoted initial abstinence (hazard ratio [HR] = 1.3) and decreased the risk of lapsing among those who achieved abstinence (HR = 1.6). The biggest effect of treatment was to prevent progression to relapse among those who had lapsed (HR = 7.1). Analysis of effects by milestones may enhance understanding of cessation treatments and their mechanisms of action.