ObjectiveNew interventions supporting health literacy and a tobacco-free lifestyle in adolescence are needed to narrow the widening gap in existing health inequalities. Health games offer potential and could be utilized for example in school healthcare, but more research is needed to increase the understanding of the effects of game elements in health interventions. The aim of this feasibility study is to determine the short-term effectiveness of the tobacco-related mobile health game Fume and a non-gamified website in comparison with a no-intervention control group, regarding tobacco-related health literacy among 10–13-year-old early adolescents. In addition, we compare the demand for and acceptability of Fume to that of the website. MethodsIn total, 151 early adolescents participated in this single-blinded, three-armed cluster randomized trial. The participants from three municipalities in southwest Finland were randomly allocated between a group with access to the health game Fume (n = 61), a group with access to the website (n = 47), and a group with no intervention (n = 43). The intervention groups first participated in a 20-min training session with Fume/the website, and then had two weeks to use Fume/the website based on their own interest. Short-term effectiveness was measured by primary (anti-smoking self-efficacy) and secondary (smoking outcome expectations, attitudes towards tobacco use, tobacco-use motives, motivation to decline tobacco use in the future, and knowledge about tobacco) outcomes derived from the theory-based determinants of tobacco-related health literacy and evaluated with self-assessment questionnaires at baseline and post-intervention (after a two-week follow-up). For evaluating the demand, the actual use of Fume/the website was tracked during the two-week period. Regarding acceptability, the raised interest towards Fume/the website and opinions about the interventions were evaluated post-intervention. Differences were tested with the McNemar, Fisher exact, and non-parametric tests. ResultsStatistically significant favorable changes during the study period were found for positive (P = 0.002) and negative (P = 0.02) smoking outcome expectations and attitudes towards cigarette smoking (P = 0.01) within the group using Fume. No statistically significant changes were detected within the website or control groups. Statistically significant differences were not found for the change in outcome variables among the three groups. The number of visits (P < 0.001), number of separate visit days (P < 0.001) and total duration of use (P < 0.001) were larger for the group using Fume than for that using the website. Fume sparked more interest in early adolescents than the website did (P < 0.001). There were no statistically significant differences in opinions about Fume and those regarding the website. ConclusionsThe intervention with embedded game elements, the health game Fume, was found to be more feasible as a tobacco-related health education intervention than the non-gamified website among early adolescents in light of demand and acceptability (raised interest). Even though no change in anti-smoking self-efficacy was found, the results of this feasibility study demonstrated favorable short-term changes with Fume in some other theory-based determinants of tobacco-related health literacy.