Moreover, taking into account numerous clinical studies and experimental data showing that the pathogenesis of depression is not limited to the brain, but may also result from an impaired cross-talk between the central nervous system and other systems in the body, particularly the immune, endocrine and digestive systems, therapeutic GLP-1 analogs such as exendin-4 or liraglutide can also normalize their functioning in many cases, thus preventing the occurrence of maladaptive brain changes associated with depressive symptoms. Here, GCG is linked to major depressive disorder.