The inclusion of nonsmokers was important to clarify whether the effects of nicotine on smokers was due to smoking withdrawal. The findings help explain the increased smoking prevalence rates and reduced quit rates associated with ADHD. Knowledge about nicotine's effects on behavioral regulation can help to develop successful smoking cessation programs for individuals with ADHD. The findings on cardiovascular activity may help determine the potential risk for cardiovascular disease in smokers and nonsmokers with ADHD. The study contributed to understanding nicotine's effects on behavioral regulation in a highly vulnerable population such as people with ADHD.