Provided are: an agent for suppressing an undesirable effect of an opioid-type analgesic (opioid), which comprises a compound having adenosine A 2A receptor antagonistic activity or a pharmaceutically acceptable salt thereof as an active ingredient； the agent for suppressing an undesirable effect of an opioid-type analgesic (opioid), wherein the undesirable effect of the opioid-type analgesic (opioid) is analgesic tolerance or constipation； the agent for suppressing an undesirable effect of an opioid-type analgesic (opioid), wherein the undesirable effect of the opioid-type analgesic (opioid) is analgesic tolerance； and the like.
