Clinical studies have also reported that patients with anhedonia have elevated levels of proinflammatory cytokines (e.g., IL-6, IL-1β, and TNF-α) compared to patients without anhedonia in depression [49, 50] several lines of evidence support a role for inflammation in the pathophysiology, etiology, and treatment outcomes of anhedonia in depression [51]. This evidence concerns the gene IL1B and major depressive disorder.