This capstone aims to examine the relationship between cigarette smoking and illicit drug use, with a specific focus on crack cocaine use among U.S. adults using 2021 National Survey on Drug Use and Health (NSDUH) data. The Social Ecological Model guides the study and seeks to understand how tobacco use is associated with other substance use behaviors while accounting for important demographic, socioeconomic, and health-related factors. This research is important because cigarette smoking and illicit drug use often occur together. Yet, the strength of this relationship, particularly with crack cocaine, has not been widely studied using recent nationally representative data. Understanding this association can help identify cigarette smoking as a potential indicator of higher-risk substance use patterns and support more effective prevention and intervention strategies. Overall, the capstone highlights the need for coordinated public health approaches that address multiple substance use behaviors together rather than in isolation. These findings suggest that tobacco use screening may be useful in identifying individuals at higher risk for other substances. Integrating tobacco control with broader substance use prevention efforts could improve early intervention and reduce long-term health consequences. In addition, addressing shared risk factors across substances may strengthen the effectiveness of public health programs. Future research could further explore how these relationships vary across different populations and social contexts.