Tramadol is a prescription medication used to treat moderate to moderately severe pain. It is a synthetic opioid analgesic that works by changing the way the brain and nervous system respond to pain. It is usually taken orally, but it can also be administered intravenously or intramuscularly. Common side effects include nausea, constipation, dizziness, drowsiness, headache, and dry mouth. It is important to follow your doctor's instructions when taking this medication.