Depression and Inflammation: A Review of the Bidirectional Relationship

Major depressive disorder (MDD) is one of the most common causes of disability globally. While MDD has long been explored through psychological and neurochemical perspectives, recent evidence suggests that inflammation plays an important role in its development and persistence. This review aims to explore the two-way relationship between depression and inflammation. It examines how depressive symptoms can trigger inflammatory processes, and how, in turn, inflammatory responses may contribute to the onset or worsening of depressive symptoms. Key biological mechanisms such as hypothalamic-pituitary-adrenal (HPA) axis dysregulation, altered tryptophan metabolism, and immune activity within the brain are highlighted. Understanding this connection carries clinical relevance-especially for the development of targeted treatment strategies. Though the potential for anti-inflammatory therapies appears promising, challenges remain due to the complex nature of MDD. Further research is essential to refine our understanding and improve clinical outcomes.