Nearly one in five US adults are diagnosed with depression at some point in their lives. As the use of antidepressants have steadily risen since their introduction in the 1980s, what have we learned about depression? Is depression truly a “chemical imbalance” of the brain? And why do antidepressants work for some people and not others? Sanjay talks to Dr. Charles Raison, a professor of psychiatry at the University of Wisconsin-Madison, about what we now believe causes depression, and most importantly, what this means for how we treat the illness - from SSRIs to psychedelics and other emerging therapies.