The present invention relates to a method for decreasing the psychotomimetic side effects and enhancing the antidepressant-like effects of ketamine by the combination of ketamine with a methylglycine derivative. The present invention also relates to a method for depression treatment comprising administrating ketamine combined with a methylglycine derivative. The present invention further provides a method for preventing or treating addictive disorders of ketamine by administrating a methylglycine derivative.