How do dopamine antagonist help opioid nausea if opioid nause is mediated through opioid receptors and not dopamine?

interrelated: All receptor systems are interrelated and interact with each other. Whatever induces nausea, the reaction is triggered by dopaminergic pathways in a part of the brain called the chemoreceptor trigger zone. Most anti-emetics work by antagonizing dopamine. The combination of opioids and antinausea medications is quite common, both for synergism and to reduce nausea.