Oxycodone affects everyone differently, but its effects include pain relief, dizziness or fainting, fatigue, confusion and difficulty concentrating, excitement or low mood, restlessness, muscle stiffness, constipation . Oxycodone is used to treat severe pain such as surgery, serious injury, and cancer pain. It is also used for other types of long-lasting pain when mild pain relievers such as acetaminophen, ibuprofen, and aspirin have stopped working.