This data threatens those who consider depression to be solely biological and treatable by drugs only.
Prescribing self-help books on the NHS is an effective treatment for depression, a study suggests.
Patients offered books, plus sessions guiding them in how to use them, had lower levels of depression a year later than those offered usual GP care.
The effect was seen in addition to the benefits of other treatments such as antidepressants, Scottish researchers report in the journal Plos One.
Such an approach may help the NHS tackle demand for therapy, they said.