The World Health Organization estimates that depression affects about 121 million people worldwide. Most modern antidepressants work through a common biological mechanism, which means that the differences in clinical efficacy between drugs are generally small. Current antidepressants all have a slow onset of action — typically of at least 1–2 weeks – during which time many patients, especially children, adolescents and young adults, are at an increased risk for suicide. Even newer antidepressants have tolerability issues that commonly lead to treatment discontinuation, such as nausea, insomnia, weight gain and sexual dysfunction. A sizable portion of patients (approximately 30%) fails to respond adequately to antidepressant treatment and is classified as displaying treatment-resistant depression.

New product launches across the seven major markets will see the overall market for antidepressants expand from US$11.9 billion in 2010 to $14.0 billion in 2020, reinforcing the status of the depression market as one of the largest amongst the central nervous system disorders.