Most clinical trials of antidepressants were done decades ago in people with severe depression recruited from specialist mental health services. Yet most people who take these drugs have mild to moderate depression.

We wanted to know whether a common antidepressant called sertraline works for this group. We found that, indeed, it does work, but differently from how we expected.

Prescriptions for antidepressants have risen substantially in wealthy countries over the past two decades (the rate has doubled in the past 10 years), and this has led to concerns that they are being overprescribed.

The vast majority of antidepressants are prescribed by GPs for patients with mild to moderate symptoms of anxiety or depression, even if these patients don’t have enough symptoms for a clinical diagnosis of depression or anxiety.