Opioids are widely prescribed therapies used to manage moderate-to-severe pain.  However, since their dramatic surge in usage (especially for the management of chronic non-cancer pain), there has been a staggering rise in opioid-related emergency room visits, opioid abuse, addiction, overdoses and deaths in the United States.

There is a growing body of evidence showing that opioids can cause a clinically significant medical condition known as “opioid-induced hyperalgesia” (OIH).  OIH is characterized by an increase in the sensitivity to pain and may even cause more wide spread pain in response to opioid treatments.  In addition, OIH pain may persist well after the original source of pain is removed.

Unfortunately for many medical providers, tolerance and OIH may be difficult to differentiate in clinical practice, since both can cause elevated pain levels for patients.  Tolerance is defined as the need to increase opioid doses to achieve the same analgesic effect whereas, OIH is defined as the increase in sensitivity to painful stimuli as a result of opioid use.  Thus, clinicians must be very careful to diagnose and differentiate both conditions properly since the intervention for tolerance (which is addressed by increasing the opioid dose) can actually worsen pain levels in patients with OIH.

There are many proposed mechanisms for opioid-induced hyperalgesia (OIH), however, most theories seem to support the NMDAreceptor activation model. In this model, opioids increase the NMDA receptors response to pain stimuli, while downgrading the analgesic effect of the opioid. In other words, patients with OIH who take an opioid will release specific chemical messengers after administration that lead to an increase in pain.

Treatments to manage OIH involve avoiding the offending opioid(s), changing or reducing the dose of the opioid, using an NMDA antagonist in addition to an opioid, utilizing other drug therapies like NSAIDs or implementing integrative therapies like medical foods to mitigate pain.

Opioid-induced hyperalgesia is not fully understood at this point in time, although it is clear that some patients experience more pain after receiving repeated and escalating doses of opioids.  More research and clinical studies are needed in the future to better understand how OIH develops, how it can be avoided and effectively managed.