Kappa opioid receptors (KORs) are a type of protein found in the brain and other parts of the body. They belong to the opioid receptor family, which also includes mu opioid receptors and delta opioid receptors. KORs play a role in regulating pain, mood, and stress responses by interacting with specific molecules called opioids. When activated by natural or synthetic opioids, KORs can produce effects such as pain relief and sedation. However, they may also lead to dysphoria or feelings of unease. Research on KORs is important for developing new treatments for pain and mood disorders without the addictive properties of other opioids.