Opioids work by activating opioid receptors throughout the body. When opioids bind to and activate certain types of opioid receptors, they: Reduce pain and discomfort by modifying the perception of pain signals that reach the brain; Cause an accompanying release of dopamine, an important neurotransmitter associated with reinforcing certain types of behavior. These pleasurable or rewarding feelings can strengthen the desire to use opioids repeatedly.