Compositions and methods for treating a depressive disorder or an anxiety disorder in a subject in need of such treatment are described herein. A therapeutically effective amount of a composition comprising a melanocortin 5 receptor (MC5R) peptide ligand according to the following: in a pharmaceutically acceptable carrier is administered to the subject. Xaa can be Cha or Pro. The MC5R peptide is a selective MC5R antagonist, and administration thereof to the subject can treat the depressive or anxiety disorder with clinical improvement observed in a relatively short time.