IGF1 and major depressive disorder: In contrast, peripheral IGF-1 has received far more attention in the last few decades, not just in depression [38,39,40,41,42,43,44,45,46,47,48,49], but also in other mental conditions such as schizophrenia [29,49,50,51,52,53,54,55,56] and bipolar disorder [57,58,59,60,61,62].