These inconclusive findings may be due to small sample sizes,22 different methods of detecting IGF-1,19,24 different sample sources,21,24 different times of taking the samples,18,23 the administration of psychotropic drugs,16,22 or whether or not the subjects fasted overnight.20,23 Therefore, in order to achieve a more conclusive result and provide a potential road of research in the biomarker or pathophysiology of major affective disorder, it should be necessary to perform a thoroughly literature review and summarization of current evidences of IGF-1 in major affective disorder. Here, IGF1 is linked to bipolar disorder.