Anhedonia is a major depressive disorder that results in an inability to gain pleasure from normally enjoyable experiences. It is a core symptom in depression and is also frequently seen in people suffering with bipolar depression, schizophrenia, substance-abuse disorders, Parkinson’s disease, diabetes and coronary artery disease. The habenula circuit in the epithalamus moderates dopamine, serotonin and other neurotransmitter pathways. Its role in reward processing is well established, indicating a potential therapeutic pathway target for anhedonia. G Protein-Coupled Receptor 139 (GPR139) is an orphan receptor in the habenula and a potential target for anhedonia therapeutic development.