AIMS: Reducing combustible cigarette smoking is a major public health concern. Research identifies both electronic nicotine delivery systems (ENDS) and cannabis use as factors that are related to combustible cigarette cessation. The current study examined whether using substances in similar ways (e.g., inhaling them) triggers the urge to smoke, thereby undermining attempts to quit. DESIGN: Analyses examined how using ENDS and smoking or vaping cannabis, both separately and together, were associated with reductions in daily combustible cigarette smoking among young adult smokers. PARTICIPANTS: Three waves of data from the Community Youth Development Study, including 909 participants who reported daily cigarette smoking at age 23, 26, and/or 28, were included in analyses. SETTING: Participants were dispersed throughout 48 US states. MEASUREMENTS: Latent growth modeling was used to model daily cigarette smoking over time. Models using past-month ENDS use, past-month smoking/vaping cannabis, and past-month co-use of ENDS and cannabis (using ENDS and smoking/vaping cannabis within the past month) as time-varying covariates were tested. FINDINGS: Over time, there was a tendency towards cessation of daily combustible cigarette use among this smoking sample. Smoking/vaping cannabis was associated with a decreased rate of daily combustible cigarette cessation among the sample, whereas ENDS use was associated with an increased rate of daily smoking cessation. The predicted additive effect of using ENDS and smoking/vaping cannabis was not significant. CONCLUSIONS: Among young adult daily cigarette smokers, smoking cannabis, on its own, poses a risk to quitting combustible cigarettes, while using ENDS may promote cigarette cessation, possibly through substitution.