A new study reviews twenty seven research reports investigating the impact of assistance dogs on the mental health of people before and after they received their assistance dogs. Almost 70% of the studies reported no impact of the assistance dogs on the mental health of the recipients while 30% reported some positive impact.
Herzog, Harold, "New study asks "Do assistance dogs improve mental health?"?" (2019). 'Animals and Us' Blog Posts, Psychology Today, December 7, 122. https://www.psychologytoday.com/us/blog/animals-and-us/202012/new-study-asks-do-assistance-dogs-improve-mental-health