While most research shows positive effects of gamification, the focus on its adverse effects is considerably smaller. Having this in mind, we conducted a systematic mapping study of the negative effects of game design elements on education/learning systems. The study revealed 77 papers reporting undesired effects of game design elements. We found that badges, competitions, Ieaderboards, and points are the game design elements most often reported as causing negative effects. The most cited negative effects were lack of effect, lack of understanding, irrelevance, motivational issues, and worsened performance. The ethical issue of cheating was also often reported. As part of our results, we map the relations between game design elements and the negative effects that they may cause. Our mapping study can help gamification designers make more informed decisions when selecting game design elements to be included in education/learning systems, raising awareness on potential negative effects.