Currently recruiting cigarette smokers (any level of smoking) as well as healthy controls for a study comparing breath carbon monoxide (CO) monitors. Breath carbon monoxide can be used as an indicator of recent smoking and is measured by CO monitors. Breath CO can also be used to determine abstinence from smoking. There are several breath CO monitors commercially available, including a next generation model that connects directly to a smartphone and interfaces with a mobile application. Given the importance of comparability between different CO monitors, this study involves a comparison between three monitors to assess their agreement in CO readings and detecting abstinence from smoking. Participants will present for 10 brief study visits to complete CO breath tests using three different monitors. These study visits will last approximately 10-15 minutes.

The purpose of this study is to assess the effects of N-Acetylcysteine (NAC), an over-the-counter antioxidant, to assist adult cigarette smokers with quitting and preventing relapse to smoking. This medication may help people quit smoking by reducing withdrawal symptoms, craving, and preventing relapse, but we do not know if NAC helps smokers early in their quit attempt or after they have already quit.