Fentyl is a pain relieving medicine. It is used to manage persistent, moderate to severe chronic pain that requires continuous, around-the-clock opioid administration for an extended period of time. Your doctor will explain how to use Fentyl. Follow the instructions carefully to get the most benefit. The dose and duration will depend on what you are using it for and how well it helps your symptoms. Use it regularly and do not discontinue using it until the doctor tells you it is alright to stop. The most common side effects of this medicine include headache, dizziness, vomiting, nausea, abdominal pain,...