their GP will usually either offer them an antidepressant drug or put them on a waiting list for psychological therapy. These treatments are somewhat effective: each treats depression successfully in about half of cases. The problem is, there is currently no way to tell whether someone would be more likely to get better after therapy or after drugs (or a combination of the two).
A brain-based approach to mental health disorders might also help us invent new treatments.
A crucial scientific challenge of our era will be measuring the cognitive and biological changes occurring in mental health on an individual level, and mapping out their relationships with treatment outcomes.