Depression therapy is one of the largest drug therapy markets in the world today. The World Health Organization predicts that, by 2020, depression will be the second-largest cause of the global health burden. According to a report by AdvanceTech Monitor, the market for antidepressant drugs continues to grow, although the rate of growth has slowed down in recent years due to generics competition. By the end of this decade, however, several major branded antidepressants will be coming off patent, opening the door to more generic medicines to treat depression.

Global sales of branded antidepressants rose over $14 billion in 2004, with venlafaxine (Effexor) and sertraline (Zoloft) leading the way with sales of $3.3 billion each. With the expiration of several patents of leading drugs for depression, however, the market share for the generic versions of these medicines increased from 20% in 2000 to 42% in 2004, and the trend is expected to continue. Venlafaxine and sertraline are both due to lose their patents within the next 5 years, and generic versions of these drugs are already in the works and expected to be available in the United States by 2010.