Objective: Theoretical models of addictive behavior suggest that subjective effects serve as a mechanism through which substance use disorders develop. However, little is known about the subjective effects of simultaneous alcohol and cannabis use, particularly whether simultaneous use (a) heightens specific subjective effects or (b) is related to unique subjective effects relative to single-substance effects. The present study used formative, qualitative data analysis to examine patterns of responses within open-answer text response data on subjective effects of simultaneous use. Method: College students who simultaneously use alcohol and cannabis (N = 443; 68.2% female) were asked to describe how alcohol effects differ on simultaneous alcohol and cannabis use versus alcohol-only use days. Results: Conventional content analysis revealed nine concepts related to simultaneous (vs. alcohol-only) use subjective effects including as follows: (a) increased/decreased impairment, (b) low arousal/relaxation, (c) balancing/replacement effects, (d) "cross-faded" effects, (e) little-tono differences, (f) altered sensation and perception, (g) increased negative affective states, (h) increased appetite, and (i) increased/decreased negative consequences. Increased impairment (N = 191) and increased relaxation (N = 110) were the most often endorsed subjective effects, followed by decreased impairment (N = 55), balancing/replacement effects (N = 50) and cross-faded/enhancement effects (N = 44). Conclusions: Subjective effects from simultaneous use largely map onto domains of single-substance alcohol and cannabis effects (e.g., relaxation, sociability, cognitive/behavioral impairment), but also include distinct domains related to simultaneous use (e.g., balancing/replacement effects, altered sensation and perception). Future quantitative research is needed to validate measures of subjective effects from simultaneous use and their relations with use behavior. [ABSTRACT FROM AUTHOR]