Provided are: an agent for suppressing an undesirable effect of anopioid-type analgesic (opioid), which comprises a compound having adenosineA2Areceptor antagonistic activity or a pharmaceutically acceptable salt thereofas anactive ingredient; the agent for suppressing an undesirable effect of anopioid-type analgesic (opioid), wherein the undesirable effect of the opioid-typeanalgesic (opioid) is analgesic tolerance or constipation; the agent forsuppressing an undesirable effect of an opioid-type analgesic (opioid),whereinthe undesirable effect of the opioid-type analgesic (opioid) is analgesictolerance;and the like.