The prevalence of chronic pain is very high in the US at approximately 30%. More than 10% of adults report having daily pain. Opioid pain medications [such as morphine] are prescribed for some pain conditions and, since they are very addictive, they can be used inappropriately and abused, to the point of causing overdose and death. This is currently a significant problem in the US and worldwide. Research on changes in the brain that cause addiction in pain patients is complicated, also because it is difficult to separate the effect of the drugs that cause addiction from the direct effect of pain on the brain. Studies in animals have found that pain per se can change the brain in ways that increase the risk of becoming addicted to pain medications. Therefore, we think that patients who have chronic pain and are prescribed opioid pain medications to treat surgery-related pain after surgery, although they never took opioids for a long time in their life, may be at increased risk of using too much opioid medications, and using opioids for a longer time than expected to treat their surgical pain.