How come pain killers make me nauseous?

Common Side Effects: Nausea is a common side effects of pain killers assuming you are referring to narcotic pain killers such as morphine and other equivalent. Often a different narcotic pain killer will result in less nausea for certain patients. Nausea when taking such pain killers can often be controlled by a drug named ondansentron (zofran (ondansetron) is the trade name).