Opioid analgesics, also known as narcotic analgesics, are commonly used clinically, such as morphine, pethidine and fentanyl. Their common characteristics are: analgesic effect; tolerance, dependence, addiction and whistle inhibition and other side effects. The drugs bind to opioid receptors in the central nervous system to produce analgesia. In pain treatment, opioid analgesics are mainly applied to acute pain caused by severe trauma, acute myocardial infarction, etc., as well as post-surgical pain and cancer pain. The two main problems with their use in chronic non-cancer pain are that they are often not given in the right doses for fear of addiction, and that the response to opioids is incomplete in some pain states, especially when there is neurological damage. Opioid use in pain-free people can lead to physical and mental dependence, but this does not happen in patients who need opioids for pain relief. When applying opioids in chronic pain, oral administration is usually the choice. The dosage is adjusted over a few days and then the drug is used routinely. The dosage can be increased as the patient’s pain intensifies. If a reasonable increase in dosage does not provide pain relief, or if intolerable complications occur as a result of the dose increase, consider adjusting to other therapies.