This project addresses the need for evidence about the effect of flavoring manipulation on waterpipe smokers' satisfaction, dependence, harm perception, and toxicants exposure. Specifically, in this clinical study investigators will compare the effect on flavored and non-flavored waterpipe tobacco on smoking behavior, subjective experiences and toxicant exposure among waterpipe users. Findings from this study will help informing flavor-based product regulation by the FDA.

Waterpipe (WP) tobacco smoking (a.k.a. hookah, shisha, narghile) is increasing rapidly in the United States (US), particularly among young people. Evidence suggests that WP smoking can lead to dependence, other tobacco use, and many of the known smoking-related diseases including cancer, cardiovascular disease and adverse pregnancy outcomes. These alarming trends led the Food and Drug Administration (FDA) in 2014 to propose including the WP under its regulatory authority, allowing the FDA to apply evidence-based regulatory approaches to control WP spread in the US. Given the salience of flavored tobacco in shaping the "WP experience", regulating WP tobacco flavor represents a promising approach for the FDA to curb WP use among US youth. This project aims to assist the FDA in these efforts by providing answers to specific questions pertinent to the potential of WP regulation through flavor. These include: - How would flavor manipulation affect the smoking experience and satisfaction of WP users at different stages of their smoking trajectory - How would smoking non-preferred flavor or unflavored WP tobacco reflects on smokers' exposure to nicotine, and dependence; and - How would flavor manipulation influence puffing behavior and exposure to toxicants such as carbon monoxide (CO) among WP smokers. Answers to these questions will help the FDA predict the impact of flavor regulation on WP experimentation and continued use. In this study, investigators will use clinical laboratory methods to answer these questions. Two groups of WP smokers will be recruited based on their use frequency: low (Beginners) vs. high frequency (Experienced) smokers (72/group; total 144; age 18-30). Each participant will undergo 2 WP smoking sessions that differ by flavor (preferred flavor; unflavored), while measurement of WP satisfaction, dependence, harm perception, and exposure to nicotine and toxicants will be conducted. The response of WP smokers at different stages of their WP smoking trajectory (Beginners vs. Experienced) to flavor manipulation, will allow to predict the effect of limiting flavors on a wide range of WP smokers. This project promises to provide the first evidence to guide the FDA in terms of the potential of regulating WP flavored tobacco on WP uptake and use in the US.

Inclusion Criteria:

• Generally healthy individuals (determined by physical examination).
• Age of 18-30 years.
• Is willing to provide informed consent.
• Is willing to attend the lab as required by the study protocol.
• WP smokers who smoke flavored WP tobacco.
• Have abstained from WP for 12 hours prior to each session

Exclusion Criteria:

• Report smoking cigarettes regularly (> 5 cigarettes/month in the past year).
• Report regular use of any other tobacco/nicotine product (e.g., e-cig, pipes, cigars) in the past year.
• Women who are breast-feeding or test positive for pregnancy (by urinalysis at screening).
• Individuals with self-reported history of chronic disease or psychiatric conditions.
• Individuals with history of or active cardiovascular disease, low or high blood pressure, seizures, and regular use of prescription medications (other than vitamins or birth control).