Study Shows Chronic Pain Linked to Opioid Use Disorder

woman holding back with chronic pain
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Over the past two years, the attention of the nation has been on the COVID-19 pandemic. As well it should have been. This once-in-a-century pandemic – which appears to be nearing endemic status, like the flu – threatened the health and wellbeing of all our citizens. As a nation we met the challenge – albeit with our share of ups and downs – and now we’re moving to what we can think of as our new normal: yearly vaccine boosters for those who want them, and effective antiviral medication to prevent serious illness and hospitalization for those who don’t.

Meanwhile, the other epidemic never went away.

Instead, it got worse.

We’re talking about the opioid epidemic, also called the opioid crisis. If you’re not familiar with the opioid epidemic, we’ll give you a quick overview.

To read to full overview on the opioid crisis, please read the following article in the blog section of our website:

Has the Treatment Gap for Opioid Use Disorder Improved?

In the late 1990s, physicians began prescribing more opioid medication for pain. Two factors played a role in that increase. First, pharmaceutical companies produced new opioid pain medications and marketed them aggressively. Second, reputable physician’s groups published letters suggesting the use of opioids for chronic pain “should not be avoided” as a result of “focusing only on the abuse potential.” As rates of opioid prescriptions rose, rates of opioid misuse, opioid use disorder, and fatal opioid overdose rose as well.

This trend continued until 2010, when regulators tightened rules on opioid prescriptions in an effort to reverse the trend in OUD and overdose. Unfortunately, that effort backfired: without access to prescription opioids, people turned to street drugs, like heroin – which cause rates of OUD and overdose to escalate.

After a brief decline from 2017-2018, rates of fatal opioid overdose and OUD began to trend upward again in 2019, and that trend continued through – and was exacerbated by – the COVID-19 pandemic. In 2021, we recorded the most overdoses for all drugs and for opioids since we started keeping records:

  • 73,453 opioid-related overdose deaths
  • 107,306 total drug overdose deaths

That means we still have a lot of work to do in order to reverse the trend in opioid misuse and opioid overdose death. This article will discuss a paper published recently that explores a topic of critical importance: the relation between chronic pain and opioid use disorder.

Central Sensitization, Chronic Pain, and Opioid Use Disorder

Given that opioids are primarily known as a prescription analgesic – a.k.a. a pain reliever – and that overprescribing opioids for pain drove the first decade of the opioid crisis, logic tells us there must be ample research on the relationship between opioids and chronic pain.

However, while there is research indicating an association between long-term opioid prescriptions and opioid use disorder, what we lack is an exploration of the underlying mechanisms related to chronic pain and how they may increase risk of opioid use disorder.

A new peer-reviewed journal publication called “Central Sensitization in Opioid Use Disorder: A Novel Application of The American College of Rheumatology Fibromyalgia Survey Criteria” seeks to fill this gap in our in our knowledge by examining the relationship between a neurological phenomenon associated with chronic pain called central sensitization and opioid use disorder.

First, let’s define central sensitization and its association with chronic pain. The International Association for the Study of Pain (IASP) offers the following definition:

“Central sensitization is the increased responsiveness of nociceptive neurons in the CNS to their normal or subthreshold input.”

Here’s a simplified definition:

“Central sensitization (CS) is a condition in which the nervous system becomes continually stimulated which causes intensified pain sensations. It is associated with chronic pain progression due to an increased response to neurons in the central nervous system.”

And here’s a definition that’s oversimplified, but accurate:

“Central sensitization, in short, is a hypersensitivity to stimuli from things that are not typically painful.”

With those definitions mind, it’s easy to see why people with CS may also experience chronic pain: their nervous system tells them they’re in pain all the time, despite the absence of injury or specific stimuli that typically cause pain.

Now let’s take a look at that study.

The OUD Connection: How Scientists Conducted the Research

One reason we’re surprised at the lack of research exploring the relationship between chronic pain and opioid misuse is that the consequences of chronic pain overlap with many of the risk factors for substance misuse in general, such as:

  • Stress
  • Anxiety
  • Depression
  • Sleep disturbances
  • Decreased quality of life
  • Impaired cognitive function

There’s another piece of the puzzle here. Most of the items on that list also meet the criteria for withdrawal symptoms of OUD. These convergences make this research more valuable, because unpacking these associations may allow clinicians and therapists to do two things: identify people at high risk or OUD, and create targeted interventions that address chronic pain and support addiction recovery.

To explore these important subject area, researchers collected data from 141 people who met the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for opioid use disorder (OUD). The DSM-5 is the go-to diagnostic manual for mental health disorders, including substance use disorder (SUD), which includes opioid use disorder (OUD).

During the study, researchers administered surveys to collect data on the following metrics:

Chronic Pain Severity

To measure severity of chronic pain, researchers used the following survey:

Chronic Pain Interference in Daily Life

To measure the extent to which chronic pain impacts daily life, researchers used the following survey:

  • The Brief Pain Inventory (BPI)
    • This survey measures affective interference, or the level at which pain has a negative impact on:
      • Sleep
      • Relationships
      • Life enjoyment
      • Mood
    • This survey also measures activity interference, or the level at which pain has a negative impact on:
      • General activity
      • Normal work
      • Walking

Quality of Life

To measure the impact of chronic pain on daily life, researchers used the following survey:

Beliefs About Pain and Expectations of Care

To learn about participant beliefs about pain and treatment expectations, researchers created two original surveys. One assessed participant beliefs about pain and OUD, and the other assessed expectations regarding treatment and care.

  • Beliefs About Pain
    • Participants rated statements on a scale of 1-5, where 1 means strongly agree and 5 means strongly disagree. Participants rated these statements about pain:
      • I first started using opioids because I was in pain.
      • Pain is a major reason why I have kept using opioids.
      • I find myself needing more and more opioids to control my pain.
      • It is possible for opioids to make pain worse over time.
    • Care Expectations
      • Participants use the same 1-5 scale applied to the Beliefs About Pain statements to rate the following statements about care:
        • Once doctors know you have an addiction, they won’t help you with your pain.
        • I have put off going to the doctor for my pain because I do not want treated like a drug addict
        • I’ve put off getting treatment for opioid use disorder because I am afraid my pain will be worse when I stop using opioids.
        • I worry pain will cause me to relapse in the future.

Understanding the way researchers conduct these studies is important because it gives us an insight not only into what we learn, but how we learn it. We know evidence-based therapeutic techniques are reliable because we spend years immersed in peer-reviewed papers like the one we’re describing right now. However, we know that most people who will read this article are not research scientists. Therefore, in order to explain what evidence-based research really means, we take time to explain these studies, and give you a look under the hood at the work that creates the data.

The Results: Does Central Sensitization Increase Chronic Pain Complications and Risk of Opioid Overuse?

This is one of those rare instances when the experimental data and results confirm almost everything hypothesized by the study authors and designers. We repeat: in a study with multiple metrics and various potentially confounding factors, this almost never happens. This study is an exception to the rule and to the way most science works.

First, a reminder: researchers hypothesized that central sensitization (CS) would be prevalent among people with OUD, and that the presence of CS would be associated with higher levels of pain interference and decreased quality of life, as well as inform or influence their beliefs about pain and their expectations for care.

To identify the presence of CS among study participants – all of whom met criteria for OUD – researchers used the ACR 2011, which also measures cognitive problems, fatigue, and sleep issues. Here’s what they found:

  • 88% reported chronic pain
    • 70% reported chronic low back pain
    • 32% reported chronic neck pain
    • 31% reported chronic upper back pain
  • 44% reported severe cognitive impairment
  • 61.7% reported excessive fatigue
  • 93% reported sleep issues

That’s the first part of the hypothesis, confirmed: CS is strongly associate with OUD.

Now let’s look at the impact of CS on daily life, quality of life, and beliefs about pain/expectations for care, as measured by the Brief Pain Inventory (BPI), the RAND-36 Quality of Life Survey, and the original surveys created by the research team.

Here’s what they found:

Pain Interference

  • Participants with CS reported significant pain interference with:
    • General activity
    • Affective metrics, including:
      • Sleep
      • Relationships
      • Life enjoyment
      • Mood
    • Specific activity, including:
      • Walking
      • Typical work

Quality of Life

  • Participants with CS reported pain negatively impacted the following quality of life domains:
    • General health
    • Mental health
    • Social functioning
    • Physical functioning
    • Vitality
    • Bodily pain
    • Emotional functioning

Beliefs About Pain and Treatment Expectations

  • Presence of CS was significantly associated with:
    • Pain-related onset of OUD
    • Opioid induced pain sensitivity
    • Stigma-related treatment delay
    • Worry that OUD treatment would increase pain
    • Worry that pain would lead to OUD relapse
  • Presence of CS was not associated with the idea that doctors would treat participants differently if they knew they had OUD
    • This is the only significant component of the hypothesis not confirmed by experimental data

Now let’s get to the data that ties it all together. Confirmation of the hypotheses above is encouraging, but not surprising, given the wealth of experiential knowledge connecting chronic pain and overall functioning. The data we really want to see will answer this question:

Is CS associated with OUD?

Here’s what they found:

  • The presence of severe CS – i.e. high levels of chronic pain – as measured by the ACR 2011, was associated with:
    • Onset of OUD
    • Maintenance of OUD
    • Escalation of OUD
    • Delayed treatment for OUD
    • Relapse to OUD

That’s an important set of results. Although previous research shows that people with chronic pain and OUD are more likely to relapse than people without chronic pain, this is the first time researchers published data connecting chronic pain with the onset, maintenance, escalation, and delayed treatment for OUD.

Interviewed in the online magazine Science Daily, Dr. O. Trent Hall, a senior author of the paper, described the results this way:

“Our study provides the first evidence of central sensitization underlying the chronic pain and OUD relationship and demonstrates a new tool for easily measuring central sensitization among individuals with OUD.”

That’s a major step in our understanding of the underlying neural mechanisms that contribute to OUD among people with chronic pain.

How This Information Helps

This data gives us valuable insight into how chronic pain – and specifically the presence of central sensitization – may impact the entire experience of a person with OUD.

In the future, this information can help researchers:

  • Explore and fully define the mechanisms common to OUD and chronic pain
  • Explore the potential of “precision treatment” that targets the underlying neurophysiological connections between chronic pain and OUD
  • Design long-term, large-scale studies that clarify “the role of CS in the onset, maintenance, escalation, and relapse of OUD.”

In the here and now, this information can help clinicians:

  • Enhance screening practices to include chronic pain metrics
  • Tailor treatment to account for the presence of CS and chronic pain
  • Tailor medication to treat pain without increasing risk of relapse
  • Design aftercare plans to account for increased risk of relapse among people with OUD and CS
  • Collaborate with people with OUD and CS to create robust social support networks that include people who have OUD and CS

If a person enters treatment for OUD afraid their pain will interfere with their recovery, clinicians can allay those fears by informing them they can account for the presence of CS and chronic pain during treatment and help them manage their recovery despite the obstacles created by CS and chronic pain. In other words, this research can contribute to something crucial to the recovery process: it can replace fear with hope.

That’s huge.

When a person in treatment has hope for the future and confidence their treatment can work, outcomes improve.

We know, because we see it happen every day.