Gamification has become a popular and promising tool to positively impact the usage of health behavior change support systems (HBCSSs). Fun and engaging components are purposefully integrated in the design of HBCSSs in an effort to encourage users to employ the system in a more regular manner or over a longer period of time. Although extant research has made extensive efforts to understand the psychological and behavioral outcomes of gamification, its potential unintended side effects have been mostly neglected. We approached this gap by reviewing 33 articles on gamification in HBCSSs. We identified 16 potential unintended side effects in five categories. By taking a critical view, our research contributes to a more nuanced approach to gamification, which helps to understand how it can be utilized as a valuable tool for developers that motivates and does not harm users of HBCSSs.