I’ve posted earlier a link to a review article on the health benefits of Taiji and Qigong in general. There is also a review article that focuses on Taiji’s impact on psychological wellbeing that was published in May 2010 in BMC Complementary and Alternative Medicine.
The Author reviewed 40 clinical studies published in English or Chinese, in which a total of less than 4,000 subjects practiced Taiji at various lengths (1 hour to 1 year). Though these studies are of varying quality, a majority of them showed that taiji practice significantly reduced stress, anxiety, depression and mood disturbance, and increased self-esteem.
You can access the full article by clicking on its title here: “Tai Chi on psychological well-being: systematic review and meta-analysis.”