Application of ketamine to treatment of major depressive disorder

The invention provides an application of a combined drug composition of ketamine or S-(+)-ketamine or a pharmaceutically acceptable salt of ketamine or S-(+)-ketamine, and escitalopram or a pharmaceutically acceptable salt of escitalopram, to the preparation of drugs for treating major depressive disorder. The major depressive disorder can be major depressive disorder breaking out for the first time, major depressive disorder breaking out again or refractory depression. The invention furthermore provides an application of ketamine or S-(+)-ketamine or the pharmaceutically acceptable salt of ketamine or S-(+)-ketamine to the preparation of the drugs for treating the major depressive disorder, and a drug preparation containing ketamine or S-(+)-ketamine or the pharmaceutically acceptable salt of ketamine or S-(+)-ketamine, and escitalopram or the pharmaceutically acceptable salt of escitalopram. Ketamine and conventional antidepressants are used together; and a proper amount of ketamine is intravenously injected once at first day of start of treatment, so that the anti-depression effect of oral antidepressants can be effectively improved, the effect display lag period is remarkably shortened, and suicidal actions of patients can be remarkably reduced.