
Pain is the leading cause of disability in the US, affecting more than cancer, diabetes and heart disease combined. Current analgesics for persistent pain are relatively ineffective, are associated with significant adverse effects or abuse liability, and do not reduce pain in all treated individuals. Opioids (e.g., morphine, codeine, oxycodone) are currently one of the most potent groups of analgesics used clinically, with prescriptions increasing by 50% over the past 10 years for chronic, non-cancer pain. However, there is clear evidence that as opioid prescription rate rise, there is a corresponding increase in opioid overdose deaths, misuse and addiction. These adverse effects are attributed to the opioid agonist effects on central opioid receptors—causing dependence, tolerance, sedation, and respiratory depression.