Tramadol is an opioid pain reliever often doctors prescribe to treat moderate to severe pain. When other pain medications are ineffective, it is widely prescribed to effectively relieve the symptoms of moderate to severe pain, such as back pain, cancer pain, and surgery pain. Buy Tramadol Online. It is available in a combination formulation (acetaminophen/paracetamol) and comes in both immediate-release (IR) and extended-release (ER) formulations. This medication has an immediate effect and a 3 to 4-hour active duration.