Opioid-induced hyperalgesia (OIH) is a condition where patients exposed to opioids for pain relief end up more sensitive to pain, a counterintuitive effect where opioids lose their efficacy. This heightened sensitivity to pain can be similar to or differ from the patient’s original pain. Despite the lack of widespread clinical data on its prevalence, various studies involving different groups, such as former opioid addicts, surgical patients and healthy volunteers, have explored OIH’s significance and manifestation. The underlying molecular mechanisms of OIH are complex and not fully understood but are believed to involve neuroplastic changes in the nervous system, leading to increased pain sensitivity. Several mechanisms, including alterations in the central glutaminergic system and spinal dynorphins, have been identified as key contributors to this condition.

Clinicians are advised to consider OIH in patients whose opioid treatment becomes less effective over time, especially if new or worsening pain develops without an apparent reason or if pain escalates with higher opioid doses. Strategies for managing OIH include reducing opioid dosage, gradually discontinuing opioids or using NMDA receptor modulators to counteract the condition. This approach points to the importance of recognising OIH early and adjusting treatment plans accordingly to manage pain effectively while minimising the risk of increased pain sensitivity due to opioid exposure.

First observed in the 19th century, OIH gained scientific attention in the 20th century. It occurs when opioids, which normally alleviate pain by interacting with brain and spinal cord receptors, end up causing heightened pain sensitivity due to long-term use.

Patients undergoing opioid addiction treatment with full agonists like methadone or partial agonists like buprenorphine often experience significant hyperalgesia. Research indicates that methadone-maintained patients, for instance, show greater sensitivity to experimental pain than drug-free controls. This increased pain sensitivity can complicate the recovery process, particularly for those transitioning from short-acting opioids like heroin to long-acting substitution therapies.

Managing OIH involves considering alternative pain management strategies that minimise opioid use. This may include non-opioid medications, physical therapy and psychological interventions. The phenomenon points to the need for tailored pain management approaches in opioid addiction treatment and recovery. While OIH is specific to opioid use, it should not discourage individuals from seeking treatment, as the addiction recovery community is focused on improving pain management for those in recovery.

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