The interactivity and attractiveness of video games are increasingly deployed for educational and training purposes in what are called “serious games.” This paper describes Happy Farm, a serious game targeting young people and aimed at increasing their awareness of the risks connected to the consumption of psychoactive substances. The development of the game is driven by the premise that credibility and usability are pre-conditions for persuasion. The achievement of these qualities is pursued in the design and is generally testified by the results of the users' evaluation. Suggestions for the improvement of the game are also outlined.