Pain and Addiction: The Neuroscience of Chronic Pain and Substance Use

Introduction

Chronic pain and addiction are among the most prevalent and debilitating conditions in modern medicine, and they are deeply intertwined. People with chronic pain have elevated rates of substance use disorders; people with substance use disorders have elevated rates of chronic pain. The opioid crisis has made this relationship tragically visible — millions of people who were prescribed opioids for legitimate pain conditions developed opioid use disorder, while millions of people with opioid use disorder struggle with undertreated pain.

Understanding the neurobiological relationship between pain and addiction is essential for providing effective, compassionate care for people who live with both conditions — and for developing treatment approaches that address both without sacrificing either.

Key Definitions

Chronic pain: Pain that persists beyond the expected healing time, typically defined as pain lasting more than 3 months. Involves changes in the central nervous system that are distinct from acute pain.

Central sensitization: A state of heightened sensitivity of the central nervous system to pain signals, in which the pain system becomes amplified and dysregulated. Common in chronic pain conditions.

Opioid-induced hyperalgesia (OIH): A paradoxical increase in pain sensitivity that can develop with long-term opioid use, driven by neuroadaptation in the opioid and glutamate systems.

Allodynia: Pain produced by stimuli that do not normally cause pain (such as light touch). A manifestation of central sensitization.

Comorbidity: The co-occurrence of two or more conditions in the same individual. Chronic pain and addiction are highly comorbid.

Scientific Background: Shared Neurobiology of Pain and Addiction

Pain and addiction share overlapping neurobiological mechanisms, which helps explain their frequent co-occurrence:

Shared brain circuits: The brain regions involved in pain processing — including the anterior cingulate cortex, insula, amygdala, and prefrontal cortex — overlap extensively with those involved in addiction. The anterior cingulate cortex, for example, processes both the emotional component of pain and the craving associated with addiction.

Shared neurotransmitter systems: The opioid system, which is central to both pain modulation and addiction, is the most obvious shared system. But dopamine, serotonin, norepinephrine, and glutamate systems are also involved in both pain processing and addiction.

Shared stress response: Both chronic pain and addiction dysregulate the HPA axis stress response system. Chronic pain activates the stress response, which in turn amplifies pain perception — a vicious cycle. This stress dysregulation also increases addiction vulnerability.

Negative reinforcement: Both pain relief and addiction involve negative reinforcement — behavior reinforced by the removal of an aversive state. Substances that relieve pain are powerfully reinforcing, particularly for people with chronic pain, because they provide relief from a persistent aversive state.

How Chronic Pain Increases Addiction Risk

Chronic pain increases addiction risk through multiple mechanisms:

Self-medication: People with chronic pain may use substances — particularly opioids, alcohol, and cannabis — to manage pain that is inadequately treated by conventional means. This self-medication can lead to dependence and addiction.

Shared vulnerability factors: The same genetic and neurobiological factors that increase pain sensitivity may also increase addiction vulnerability. For example, variants in the mu-opioid receptor gene (OPRM1) affect both pain sensitivity and opioid response, influencing both chronic pain risk and addiction risk.

Psychological factors: Depression, anxiety, and PTSD — which are common in people with chronic pain — also increase addiction risk. The psychological burden of chronic pain may drive substance use as a coping mechanism.

Iatrogenic addiction: Prescription opioids, while effective for acute pain, carry significant addiction risk with long-term use. The widespread prescription of opioids for chronic pain conditions has contributed substantially to the opioid epidemic.

Opioid-Induced Hyperalgesia

One of the most important and counterintuitive findings in pain and addiction neuroscience is opioid-induced hyperalgesia (OIH) — a paradoxical increase in pain sensitivity that can develop with long-term opioid use. OIH means that the very medications prescribed to treat pain can, over time, make pain worse.

The neurobiological mechanisms of OIH include:

• Activation of NMDA glutamate receptors, which amplify pain signals in the spinal cord.
• Upregulation of dynorphin — an endogenous opioid that activates kappa opioid receptors and produces dysphoria and pain sensitization.
• Neuroinflammation in the spinal cord, driven by opioid activation of glial cells.
• Downregulation of mu-opioid receptors, reducing the analgesic efficacy of opioids while sensitizing pain pathways.

OIH is clinically important because it means that increasing opioid doses in response to worsening pain may actually worsen the underlying pain condition. Recognizing OIH and considering opioid tapering — counterintuitive as it may seem — can sometimes improve pain outcomes.

Addiction and Pain Amplification

Just as chronic pain increases addiction risk, addiction can amplify pain. Several mechanisms contribute to this:

Withdrawal hyperalgesia: Opioid withdrawal produces a state of heightened pain sensitivity — withdrawal hyperalgesia — that is one of the most distressing aspects of opioid withdrawal and a major driver of relapse. The pain of withdrawal is not simply the absence of opioid analgesia; it reflects active pain sensitization produced by the neurobiological rebound of opioid cessation.

Alcohol and pain: While alcohol acutely reduces pain sensitivity, chronic alcohol use produces central sensitization and increased pain sensitivity. People with alcohol use disorder often have elevated pain sensitivity compared to non-drinkers, and alcohol withdrawal is associated with hyperalgesia.

Emotional pain: The emotional pain of addiction — shame, loss, grief, isolation — activates the same brain circuits as physical pain. The anterior cingulate cortex processes both physical and social/emotional pain, and the opioid system modulates both. This overlap may explain why social rejection and emotional pain are such powerful triggers for substance use.

Clinical Implications: Treating Co-Occurring Pain and Addiction

Treating co-occurring chronic pain and addiction requires an integrated approach that addresses both conditions:

Multimodal pain management: Effective pain management for people with addiction should prioritize non-opioid approaches — physical therapy, cognitive behavioral therapy for pain, anti-inflammatory medications, nerve blocks, and neuromodulation techniques. When opioids are necessary, they should be used at the lowest effective dose with careful monitoring.

Buprenorphine for co-occurring pain and addiction: Buprenorphine — the partial opioid agonist used for opioid use disorder — also has analgesic properties and can be an effective treatment for people with co-occurring opioid use disorder and chronic pain. It provides stable opioid receptor occupancy that reduces both craving and pain, without the peaks and troughs of short-acting opioids.

Psychological approaches: Acceptance and Commitment Therapy (ACT) and CBT-based pain management approaches can help people with chronic pain develop psychological flexibility and coping skills that reduce the suffering associated with pain without relying on substances.

Exercise: Regular exercise is one of the most evidence-based treatments for both chronic pain and addiction. It reduces pain through multiple mechanisms — including endorphin release, anti-inflammatory effects, and central sensitization reduction — while also supporting addiction recovery through its effects on the dopamine system and stress response.

Frequently Asked Questions

Can people with addiction receive opioids for pain?
Yes, but with careful consideration and monitoring. People with opioid use disorder who require opioids for pain management should ideally be treated by providers experienced in both pain management and addiction medicine. Buprenorphine is often the preferred option as it treats both conditions simultaneously.

Does cannabis help with chronic pain?
Research suggests that cannabis can reduce pain intensity in some chronic pain conditions, particularly neuropathic pain. However, the evidence base is limited, and cannabis use carries risks including addiction, cognitive impairment, and psychiatric effects. For people with a history of substance use disorders, the risks of cannabis use for pain management require careful consideration.

Why does pain get worse in opioid withdrawal?
Opioid withdrawal produces withdrawal hyperalgesia — a state of heightened pain sensitivity — through multiple mechanisms including NMDA receptor activation, dynorphin upregulation, and neuroinflammation. This withdrawal-related pain amplification is one of the most powerful drivers of relapse in people with opioid use disorder.

Key Takeaways

• Chronic pain and addiction share overlapping neurobiological mechanisms, including shared brain circuits, neurotransmitter systems, and stress response dysregulation.
• Chronic pain increases addiction risk through self-medication, shared vulnerability factors, and psychological burden.
• Opioid-induced hyperalgesia — a paradoxical increase in pain sensitivity with long-term opioid use — is an important clinical phenomenon that can worsen pain outcomes.
• Treating co-occurring pain and addiction requires an integrated approach that addresses both conditions simultaneously.
• Buprenorphine, multimodal pain management, psychological approaches, and exercise are evidence-based treatments for co-occurring pain and addiction.

Additional Resources

Related articles on Sobriety Navigator: The Opioid System and Addiction, Opioid Use Disorder, Medication-Assisted Treatment, Stress and Addiction.