It is estimated that only 30-40% of people with depression get better after eight weeks of treatment with an antidepressant. Doctors don't always know which one will work. They can take a while to work while they are absorbed by the body and some patients do not improve until the dose is raised above the starting level. Treatment is usually started with one antidepressant at a time so if this does not work there can be a delay before people get switched on to another, more effective one. Researchers from Columbia University in New York tried to overcome these problems by starting patients on two drugs (escitalopram and bupropion) at the same time and by increasing the doses of them much more rapidly than usual. By the end of their eight-week study 63% of the participants had remitted although 18% had dropped out because of side effects. The study was quite small (just 49 people) and had a number of methodological weaknesses but the new approach could be promising.
Stewart, Jonathan W. ... [et al] - Does dual antidepressant therapy as initial treatment hasten and increase remission from depression? Journal of Psychiatric Practice September 2009, 15(5), 337-345