Response rates for even the most well-established antidepressants are poor, rarely exceeding 30%. This is likely due to fact that depression is a heterogeneous disorder. Using the DSM-5, two patients diagnosed with depression may not share a single symptom. Antidepressants also vary considerably in their mechanism of action, and research has shown that antidepressants also differ in their ability to treat certain symptoms. Thus, there is a great need to understand which patients respond to which antidepressants.