Dynorphin A is an endogenous opioid peptide located in the central nervous system (CNS) that is a modulator of pain and immune response. It promotes emotional balance and enhanced mental activity, and reduces feelings that lead to compulsive behavior. It exerts its opioid effects primarily through the k-opioid receptor (KOR). Provides analgesia, and has a high affinity for x-receptors that mediate unpleasant dysphoric side effects of opioids, such as preventing or reversing morphine-dependent withdrawal signs and symptoms.