Whereas the smoking prevalence rates in the general population are declining, rates among people diagnosed with attention-deficit hyperactivity disorder (ADHD) continue to be elevated. Smoking may be a form of self-medication in people with ADHD, which has specific reinforcing mechanisms such as improvement of ADHD core symptoms, enhancement of moods and arousal, or a combination of both. In addition, the reinforcing effects of smoking may be potentiated by stimulant medication. The proposed study examines the reinforcing effects of ad libitum smoking with and without stimulant medication in adult smokers with clinically diagnosed ADHD. Participants will include 40 adults (20 men, 20 women) diagnosed with ADHD and treated with stimulant medication. Participants will be recruited mainly from local treatment centers and clinical practices. The effects of smoking and stimulant medication will be studied both in the laboratory and in everyday life. In the laboratory, participants will undergo the Continuous Performance Task in order to assess attention and inhibition in response to smoking a cigarette versus abstinence with and without stimulant medication. In everyday life, participants will be asked to undergo 2 conditions: ad libitum smoking with stimulant medication and ad libitum smoking with placebo pill. During each condition ADHD symptoms, moods, and arousal will be assessed with an electronic handheld diary for 2 days during waking hours in natural settings. Specifically, the electronic diary will monitor ADHD symptoms (e.g., inattention, impulsivity), moods (e.g., happiness, sadness, anger), arousal (i.e., tired, alertness), location (e.g., home, school, work), activity (e.g., read/write, talk, walk), and consumption (e.g., alcohol, caffeine, food) during smoking' and nonsmoking occasions. Smoking will be monitored by an electronic cigarette case. Such electronic monitoring is less subject to memory bias and distortions than conventional assessments and will be linked to the Continuous Performance Task in the laboratory in order to assess validity. The study will delineate the reinforcing mechanisms associated with smoking in laboratory and natural settings. Identifying the reinforcing mechanisms of smoking in interaction with stimulant medication will contribute to a better understanding of nicotine addiction and facilitate the development of targeted smoking cessation and prevention programs for individuals with ADHD and other people with deficiencies in impulse control and excessive risk taking. [unreadable] [unreadable] [unreadable]