1 3 Eur Child Adolesc Psychiatry DOI 10.1007/s00787-016-0842-5 ORIGINAL CONTRIBUTION Behavioral activation for late adolescents with subthreshold depression: a randomized controlled trial Koki Takagaki 1 · Yasumasa Okamoto 1 · Ran Jinnin 1 · Asako Mori 1 · Yoshiko Nishiyama 1 · Takanao Yamamura 1 · Satoshi Yokoyama 1 · Syouichi Shiota 1 · Yuri Okamoto 2 · Yoshie Miyake 2 · Akiko Ogata 3 · Yoshihiko Kunisato 4 · Haruki Shimoda 5 · Norito Kawakami 5 · Toshi A. Furukawa 6 · Shigeto Yamawaki 1 Received: 4 September 2015 / Accepted: 11 March 2016 © Springer-Verlag Berlin Heidelberg 2016 was the Beck Depression Inventory-II score. Results indi- cated that late adolescent students in the treatment group showed significant improvements in their depressive symp- toms (effect size -0.90, 95 % CI -1.28 to -0.51) com- pared to the control group. Students in the treatment group also showed significant improvements in self-reported rat- ing of quality of life and in behavioral characteristics. It is concluded that this intervention had a large and significant effect despite being short and simple and that this low- intensity cognitive behavioral therapy program could be conducted in many different types of institutions. It is sug- gested that the long-term effects of the treatment program should be targeted for investigation in future studies. Keywords Late adolescent · Subthreshold depression · Behavioral activation · Randomized controlled trial Introduction Subthreshold depression has recently become the focus of increasing attention [1]. It is defined by clinically signifi- cant depressive symptoms that do not meet diagnostic crite- ria for major depressive disorder [2]. The incidence of sub- threshold depression increases steadily from 12 to 20 years of age [3]. It can lead to serious functional impairments, including causing a negative impact on academic perfor- mance and social activities [4]. People with subthreshold depression are subsequently at an elevated risk for develop- ing a major depressive episode [1, 5]. Therefore, adolescent students are an important target group for interventions aimed at reducing subthreshold depressive symptoms, to prevent the development of a major depressive episode. The effectiveness of psychological treatments for sub- threshold depression has been demonstrated in a previous Abstract The main behavioral characteristic of sub- threshold depression that is observed in adolescents is the low frequency of exposure to environmental rewards. Therefore, it was considered that a simple intervention con- ducted in short sessions, focusing on increasing access to positively reinforcing activities, would be efficacious in increasing the availability of rewards. We conduct a rand- omized controlled trial to examine the efficacy of such a behavioral activation program that was conducted weekly for 5 weeks in 60-min sessions. Late adolescent univer- sity students aged 18–19 years with subthreshold depres- sion were randomly allocated to a treatment (n = 62) or a control group (n = 56). The primary outcome of the study * Yasumasa Okamoto oy@hiroshima-u.ac.jp 1 Department of Psychiatry and Neurosciences, Graduate School of Biomedical and Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan 2 Health Service Center, Hiroshima University, 1-7-1, Kagamiyama, Higashihiroshimashi, Hiroshima 739-8511, Japan 3 Department of Psychology, Hiroshima University, 1-1-1, Kagamiyama, Higashihiroshimashi, Hiroshima 739-8511, Japan 4 Department of Psychology, School of Human Sciences, Senshu University, 2-1-1, Higashi-Mita, Tama, Kawasaki 214-8580, Japan 5 Department of Psychiatry of Mental Health, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan 6 Department of Health Promotion and Human Behavior and of Clinical Epidemiology, Kyouto University Graduate school of Medicine/School of Public Health, Yoshida Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan