The present invention provides a combination medicine for treatment of depression, comprising a combination of (A1) an antidepressant and either (B1) a dopamine D1 receptor agonist or (C1) a dopamine D1 receptor antagonist and a method for screening for an antidepressant that in combination with a dopamine D1 receptor agonist provides an improvement in treatment of depression, the method comprising the steps of: administering, to a mammal, (A2) a compound having an antidepressant action and (B1) a dopamine D1 receptor agonist, and detecting a greater increase in depression-related gene expression, dopamine D1 receptor expression and/or dopamine D1 receptor signaling in comparison with the case where (A2) the compound having an antidepressant action or (B1) the dopamine D1 receptor agonist is administered.
