Use of electronic nicotine delivery systems (ENDS) and cannabis is rising, especially among young people (Johnston et al., 2019; Substance Abuse and Mental Health Services Administration, 2020). Emerging research has begun to show a potential relationship between ENDS and cannabis use, with approximately 40% of ENDS using adolescents and over 50% of ENDS using undergraduates endorsing cannabis use (Ashford et al., 2020; Evans-Polce, Veliz, et al., 2020). Further, ENDS use is prospectively related to subsequent cannabis use initiation (Dai et al., 2018; Evans-Polce, Patrick, et al., 2020; Ksinan et al., 2020; Silveira et al., 2018; Unger et al., 2016). In fact, the odds of past or current cannabis use were 3.5 times higher among young people who used ENDS compared to those that did not (Chadi et al., 2019). ENDS users were also less likely to perceive cannabis use as risky (Evans-Polce, Patrick, et al., 2020). Higher rates of cannabis use among ENDS users is concerning given that adolescents who used ENDS were more likely have a higher frequency of cannabis use compared to those who did not use ENDS (Azagba, 2018). Taken together, these data indicate that ENDS use could be a risk factor for cannabis use and for greater cannabis use; yet no known studies have tested whether the use of cannabis among ENDS users is associated with worse ENDS-related outcomes. Similarly, despite accumulating evidence of dual use of cannabis and ENDS, no known studies have tested whether ENDS use is associated with worse cannabis-related outcomes (e.g., frequency of cannabis use, continued cannabis use despite cannabis-related problems).