AP-238 is a new opioid drug 5 times more effective than morphine, it is an excellent analgesic, it is very popular in Asia for the treatment of cancer patients. AP-238 is a µ-opioid receptor (MOR) agonist with a relatively low affinity for the δ-opioid receptor and κ-opioid receptor. When used regularly, AP-238 can quickly develop drug tolerance and addiction.