chronic pain

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Pain is not just a signal from injured tissue. It is a subjective sensory and emotional experience produced by the brain, influenced by biological, psychological, and environmental factors. Two people can have the same injury but very different pain experiences because pain is shaped by factors such as beliefs, fear, stress, mood, sleep, previous experiences, and the nervous system’s sensitivity.

Types of pain

Acute pain

Acute pain is short-term pain after injury, surgery, trauma, or illness. It acts as a warning signal to protect the body and prompt help-seeking.

Subacute pain

Subacute pain is the transition phase between acute and chronic pain. This is an important window where appropriate management may reduce the risk of chronic pain developing.

Recurrent pain

Recurrent pain occurs in cycles, such as migraine or pelvic pain.

Chronic pain

Chronic pain persists beyond the expected time for healing. It may continue even after the original injury has healed, and sometimes there is no clear ongoing tissue damage. Chronic pain can become a condition or disease in its own right, because the nervous system itself becomes sensitised.

Nociceptive pain — “tissue warning pain”

Nociceptive pain starts when specialised nerve endings called nociceptors detect actual or potential tissue damage.

The pathway is:

Tissue injury or threat activates nociceptors.
Pain signals travel through peripheral nerves.
Signals enter the spinal cord through the dorsal root.
They synapse in the dorsal horn.
Signals travel upward to brain regions including the thalamus, hypothalamus, reticular system, and cortex.
The brain interprets the signal as pain.

The page 1 diagram shows this pathway from nociceptors in muscle, through the spinal cord, and up to brain regions involved in pain perception, emotion, sleep, and stress responses.

Examples include pain from:

fracture
sprain
burn
inflammation
post-operative tissue injury
arthritis flare

Neuropathic pain — “nerve injury pain”

Neuropathic pain occurs when there is injury or dysfunction in the peripheral or central nervous system itself.

It can be difficult to recognise because pain may occur in an area with reduced sensation, or in an unusual distribution. Patients may describe:

burning
shooting
electric shock-like pain
pins and needles
numbness with pain
pain from normally non-painful stimuli, such as light touch or breeze

Examples in the fact sheet include trigeminal neuralgia, postherpetic neuralgia, diabetic neuropathy, central pain after stroke or spinal cord injury, phantom limb pain, and post-surgical neuropathic pain.

How acute pain can become chronic

Untreated or undertreated acute pain can lead to changes in the nervous system through neuroplasticity.

After ongoing tissue or nerve injury:

peripheral nociceptors become more sensitive
spinal cord neurons become more reactive
the brain and spinal cord can develop a “pain memory”
pain signals may continue even after the original injury has healed

This is called pain sensitisation. The nervous system becomes over-responsive, so pain is produced more easily and may persist unnecessarily.

Gate Control Theory

The Gate Control Theory explains that the nervous system is not just a passive cable carrying pain signals to the brain.

At the spinal cord level, pain signals can be amplified or inhibited before reaching the brain. The “gate” can be more open or more closed depending on competing nerve inputs and descending signals from the brain.

In chronic pain, the gate may remain more open, allowing pain messages to continue even with normal daily activity. The brain also sends descending signals back to the spinal cord, which can either dampen or amplify pain.

Why chronic pain is more than just ongoing injury

Chronic pain is often not proportional to visible tissue damage. It may reflect a sensitised nervous system rather than ongoing structural injury.

Important concept:

Hurt does not always equal harm.

A patient may have severe pain even when investigations show minimal findings, because the pain system itself has become overactive. This does not mean the pain is “imaginary”; it means the nervous system is producing a real pain experience through altered processing.

Clinical takeaway

Pain should be understood using a biopsychosocial model:

Biological factors

tissue injury
inflammation
nerve injury
central sensitisation
sleep disruption
deconditioning

Psychological factors

fear
anxiety
depression
catastrophising
previous trauma
beliefs about damage

Social/environmental factors

work stress
family stress
compensation issues
reduced activity
isolation
cultural beliefs
access to care

The RACGP First Do No Harm guidance

– https://www.racgp.org.au/clinical-resources/clinical-guidelines/key-racgp-guidelines/view-all-racgp-guidelines/first-do-no-harm/gp-resources/opioids-to-treat-chronic-non-cancer-pain

The RACGP First Do No Harm guidance says chronic non-cancer pain is multifactorial, influenced by biological mechanisms, culture, previous pain experiences, beliefs, expectations, mood and resilience. It aligns with the PainAustralia concept that pain is a subjective brain-and-nervous-system experience, not simply a direct measure of tissue damage.

For chronic non-cancer pain, the RACGP position is:

Long-term opioids should not be common.
There is limited evidence supporting opioids for chronic non-cancer pain.
There is no evidence of long-term benefit for chronic pain outcomes.
Opioids can cause significant harm, so use must be cautious and based on individual risk–benefit assessment.

What not to do

Do not initiate or escalate opioids for chronic non-cancer pain unless all of the following have been done:

comprehensive biopsychosocial assessment
clear diagnosis
careful risk–benefit assessment
shared decision-making management plan
plan for regular clinical monitoring

Do not initiate or escalate opioids in patients with comorbid alcohol use disorder, substance use disorder, or polydrug use.

Do not abruptly stop opioids in patients already taking them for chronic non-cancer pain. Tapering should be planned, staged, and collaborative.

What to do instead

Use non-drug interventions first, and consider non-opioid analgesia where appropriate. RACGP specifically supports psychological therapies, physical therapies, return to activity, and multidisciplinary care.

Examples include:

pain education
pacing and graded activity
physiotherapy or exercise physiology
strengthening programs
hydrotherapy, yoga, Tai Chi
CBT, ACT, behavioural therapy
sleep optimisation
mood and trauma-informed care
occupational therapy
multidisciplinary pain service referral when pain continues to reduce function or quality of life

If the patient is already on opioids

RACGP recommends:

prescribe the lowest effective dose
monitor pain and function regularly
use real-time prescription monitoring
review sedating co-medications, especially benzodiazepines, antipsychotics, gabapentinoids, alcohol
develop a deprescribing plan through shared decision making unless opioids are being used for end-of-life pain or dyspnoea
consider naloxone access if overdose risk is present

Main harms of long-term opioids

Common harms include:

nausea
constipation
itch
sedation
dental caries
sexual dysfunction
low mood

Serious harms include:

falls
impaired driving
overdose
respiratory depression
cardiac arrhythmias
worsening sleep apnoea
death

Long-term use can also cause tolerance, dependence, withdrawal, opioid-induced hyperalgesia, and diversion-related harms.

Red flags for specialist or multidisciplinary review

Consider pain specialist or multidisciplinary review if there is:

opioid plus benzodiazepine use
two or more psychoactive medicines
complex mental health comorbidity
substance use history
suicidality or previous overdose
unexpected dose escalation
high distress
new patient requesting opioids without an established therapeutic relationship
correctional/forensic history
possible high-risk medication behaviour

Patient explanation

“Chronic pain is real, but it often behaves differently from acute injury pain. In long-term pain, the nervous system can become sensitised, like an alarm system that keeps ringing too easily. Opioids may help short-term severe acute pain, but for chronic non-cancer pain they usually do not improve long-term function or quality of life and can cause serious harm. The safest approach is to focus on function, movement, sleep, mood, pacing, education and multidisciplinary support.”

Resources and information for patients

NSW Government Agency for Clinical Innovation, self-management of pain resources
Pain Australia, The nature and science of pain
Pain Australia support groups and help lines
The Royal Australian College of General Practitioners, Opioids to treat long-lasting pain
University of South Australia, Professor Lorimer Moseley discusses his experience with pain for Feeling Human at MOD