[Current status and issues in clinical use of opioids]

In Japan, 14 opioids with a variety of dosage forms, such as oral preparation, injection, transdermal patch, transmucosal and suppository are clinically available as analgesics, and their use properly depends on the type and degree of pain and patient condition. Fundamentally, strong opioids are restricted to only treatment of cancer pain, while the indication of fentanyl transdermal patch and oxycodone tamper resistant tablet has been expanded for the treatment of non-cancer chronic pain. In US, the additional indication of opioids to chronic pain has led to prolongation and generalization of opioid use, which may contribute to "opioid crisis" in which opioid-related death strikingly increased due to opioid abuse and overdose-induced respiratory depression. Currently, opioid-related abuse and death have not been evident in Japan, while abuse of antitussive opioids (codeine and dihydrocodeine) are recently seen as a problem, which may suggest the sense of guilt to abuse legally-uncontrolled drugs (ex. weak opioids, antitussives or hypnotics) may be low in Japanese. In this review, I will summarize current status and issues in clinical use of opioid analgesics, and will talk about the necessity and expectation for development of novel analgesics without serious adverse reactions such as addiction and respiratory depression.