Three positive psychology interventions (coping humor, three funny things, three good things) were compared with a placebo control condition (early memories) in a randomized placebo-controlled online trial. A total of 182 healthy participants participated in a one week web-based diary study and completed evaluation measures at pre, post, and one month follow-up. They were recruited via e-mail and have been primarily students. Primary outcomes have been happiness and depressive symptoms, secondary outcomes coping humor, cheerfulness (and its subscales), and subjective perceived change. The intention-to-treat analysis (ITT) using linear mixed models could not replicate the positive effects of past research. When compared to the control condition, only the coping humor intervention influenced primary outcomes (r=0.240.29). Three funny things and three good things had no effects at all. Secondary outcomes showed only isolated effects, so that no uniform effect pattern was found for the interventions. Reasons for the small effects, such as motivation and psychosocial status of the participants, as well as recommendations for future studies are discussed.