Tramadol is a prescription medication that is commonly used to treat moderate to severe pain. It is an opioid analgesic, meaning it binds to opioid receptors in the brain to reduce the perception of pain. Common side effects of tramadol include nausea, constipation, dizziness, and headaches. It is important to follow the instructions of your doctor when taking tramadol, and not to take more or less than prescribed. It is also important to note that tramadol can be habit-forming, and should not be taken for long periods of time without medical supervision.