There are many kinds of drugs used to relieve pain in cancer patients, and strong opioid analgesics have the best effect. Cancer patients usually have obvious pain, which is called cancer pain. The best drugs for relieving cancer pain are strong opioid analgesics, which can reduce or disappear pain by agonizing opioid receptors in the central nervous system. The representative of this kind of drugs is morphine, but morphine is highly addictive, short-acting and has great side effects, so it cannot be used for a long time. At present, the better opioid painkillers include the first generation of morphine sulfate extended-release tablets, the second generation of oxycodone hydrochloride extended-release tablets, which are artificially modified morphine-based painkillers, which are not only less addictive and longer acting, but also have significantly reduced other side effects, among which the second generation of oxycodone hydrochloride extended-release tablets, with the trade name OxyContin, is one of the best painkillers. In addition, if patients cannot take oral medication due to coma and other reasons, they can also use topical painkillers such as fentanyl transdermal patch, which is a strong opioid analgesic for external use.