Experts have warned that analgesics have limited effect on low back pain – the world’s leading cause of disability, with half a billion (9%) adults affected at one time – and some, like opioids and benzodiazepines, have substantial risks.
Oral and, less certainly, topical non-steroidal anti-inflammatory drugs have small benefits that may not be outweighed by risks (particularly gastrointestinal) for short term use for low back pain, they write in The BMJ.
Reviewing what is known about common analgesics for treating non-specific low back pain, (focusing on adults between 18 and 60), they conclude that future research should include how to reduce analgesia-prescribing when benefits do not outweigh harms; how best to help people – using ineffective drugs regularly – to stop using these analgesics; and how effective analgesics are for low back pain in the immediate term (within two hours).
Acute low back pain typically improves within a few weeks without treatment; for chronic low back pain, the focus of management should be on non-pharmacological treatments to improve function and address the broader determinates of pain, they suggest.
What is low back pain?
Low back pain is felt between the lower ribs and the buttocks, differing from radicular low back pain – when a spinal nerve root is affected, resulting in pain extending down the legs.
At least 90% of cases are non-specific. The causes of the remaining 10%, affecting around <1 in 100 in primary care and about five in 100 in emergency departments, include fractures, infections, malignancies, inflammatory disorders like spondylarthritis, spinal stenosis, or non-spinal problems like kidney problems or menstrual-related pain.
The prognosis for a new episode of non-specific low back pain is good, with most people recovering within a few weeks irrespective of any treatment.
Some people, however, develop chronic low back pain (for more than three months), either as a fluctuating/recurring or continuous problem. A quarter will have some ongoing pain or functional impairment at three months (chronic pain), although estimates from individual studies range widely from 2% to 48%.
Management
Most international guidelines advise non-drug treatment and limited use of some analgesic treatments; patients should keep active (continue usual physical activities), avoid bed rest (it does not aid recovery), and use self management strategies like heat packs.
About one in five will experience major life or work limitations and may benefit from further treatment.
For people with chronic non-specific low back pain, optimal approaches use physical and psychological therapies that improve function and address psychosocial contributors to the pain.
Both prescription and over-the-counter analgesics are widely used as an alternative or addition to non-drug treatments.
Across primary care services in high income countries, 66%-89% of consultations for low back pain result in a prescription for analgesia, but there are limited prescribing data from low and middle income countries. Herbal medicines (such as topical cayenne pepper) and homoeopathy are prescribed in some settings, but vary between regions.
Efficacy of analgesia
Most commonly used analgesics offer no to small benefit versus placebo: all have a risk of harm (to varying degrees).
Paracetamol (acetaminophen)
There is moderate to high certainty evidence of no effect over placebo for both acute and chronic low back pain. A systematic review of 13 randomised controlled trials (RCTs) in Australian and Austrian cohorts of patients with low back pain found a mean difference in pain score of −0.5 (95% confidence interval −2.9 to 1.9). In patients with low back pain, there was no increased risk of harms.
However, in RCTs assessing people with osteoarthritis or low back pain, paracetamol was more likely to cause abnormal liver function tests (though the clinical importance of the changes remains unknown).
Observational data and trials in broader populations using paracetamol for any reason (such as other pain, fever) at standard therapeutic doses show a dose-dependent increase in risk of harms (cardiovascular, gastrointestinal, and renal).
Data informing these risk estimates are potentially confounded by not adjusting for concomitant use of non-steroidal anti-inflammatory drugs (NSAIDs) and by including participants who were unsuitable for NSAIDs (with cardiac, gastrointestinal, and renal risk factors), who are prescribed paracetamol as an alternative. Paracetamol is typically safe when taken as directed in people without contraindications and is generally safer than anti-inflammatories.
Non-steroidal anti-inflammatories (NSAIDs)
NSAIDs include ibuprofen, diclofenac, naproxen, and celecoxib. For acute low back pain, there is moderate certainty evidence of small benefit above placebo (mean difference in pain intensity −0.9 (95% CI −1.1 to −0.7) from six RCTs conducted in Norway, Belgium, France, Australia, and Germany) and a risk ratio of 2.5 (1.2 to 5.2) of gastrointestinal harms (28/702 participants taking NSAIDs compared with 9/465 in the placebo groups).
For chronic low back pain, there is low certainty evidence of small average benefits (mean difference −0.7 (−1.1 to −0.3, from six RCTs conducted in Italy, UK, and US).
The available data from RCTs of chronic low back pain do not report increased risk of harm compared with placebo.
However, RCTs and observational studies of populations taking NSAIDs for any reason (like osteoarthritis or rheumatoid arthritis) showed increased NSAID related adverse events (such as gastrointestinal, cardiovascular, and renal) which escalate with long term use.
Antidepressants
There are no data on antidepressants for treating acute low back pain. For chronic low back pain, there is moderate certainty evidence that serotonin-norepinephrine reuptake inhibitors (such as duloxetine) may have a small effect (mean difference −3.67 (−5.91 to −1.42) from three RCTs conducted in the US and Japan) and low certainty evidence that tricyclic antidepressants are ineffective (mean difference −0.9 (−5.4 to 3.7) from three RCTs conducted in the US and Switzerland).
Opioids
A 2023 trial in Australia in 347 patients with acute low back pain found strong evidence of no effect of oxycodone (mean difference 0.5 (0.0 to 1.1)), and worse long term outcomes (such as worse pain and a higher risk of opioid misuse) compared with placebo.
For chronic low back pain, there is moderate certainty evidence that opioids (numerous single or combination opioid formulations including morphine, tramadol alone or with paracetamol, tapentadol, oxycodone, and fentanyl) probably have a small average effect (mean difference −1.0 (−1.3 to −0.7) from 13 RCTs conducted in Germany, US, Canada, and Australia).
Despite this, opioids are not recommended to treat chronic pain because of risks of harms with long term use, including dependence, misuse, overdose, and tolerance resulting in dose escalations that may further contribute to increased risk of harms.
Anticonvulsants
There are no data on efficacy for acute low back pain, but high certainty evidence of no effect above placebo of gabapentin or pregabalin for chronic low back pain (mean difference 0.0 (−0.8 to 0.7) from 14 RCTs conducted in Australia, US, and Ireland).
Benzodiazepines
Small trials conducted in the 1970s to 1990s report some effect on acute or chronic low back pain (effect size and level of certainty not reported).
Other studies indicate that benzodiazepines do not possess meaningful analgesic properties separate from their sedative properties.
Non-benzodiazepine muscle relaxants
This category of medicine is broad and includes a variety of pharmacologically unrelated medications such as cyclobenzaprine, tolperisone, baclofen, and orphenadrine with similar indications.
In both acute and chronic low back pain, there is low and very low certainty evidence that non-benzodiazepine muscle relaxants might offer small benefits (mean difference −0.8 (−1.2 to −0.3) from 14 RCTs from the US, Finland, UK, Turkey, and India) but increase the risk of harms, primarily sedation.
Oral corticosteroids
Limited evidence suggests they may be not effective for acute or chronic low back pain (mean difference 0.6 (−2.2 to 1.0) from one RCT conducted in the US), and may not cause harm in short courses.
Cannabinoids
A single RCT of oral cannabidiol in 100 patients found no effect on low back pain compared with placebo (mean difference −0.3 (−1.3 to 0.6)) and no increase in short term harms in a hyperacute, emergency department setting. There are no data for chronic low back pain, and no data on harms associated with long term use in other chronic conditions.
Oral combination medicines
There is low certainty evidence that combining medicines does not produce superior effect sizes and may increase the risk of harms. An example of combination medicines sometimes used to treat low back pain is an opioid plus an NSAID or paracetamol.
Topical preparations
There is some indirect evidence (level of certainty not assessed) that some formulations of NSAIDS and rubefacients may reduce back pain attributed to muscle strains or sprains more than placebo (effect size not reported), which may apply to some cases of acute low back pain, with no increased risk of harms. There are no data on efficacy for chronic low back pain, but indirect evidence from other chronic pain conditions such as knee osteoarthritis has shown limited effect.
Homoeopathy
There is no reliable evidence of efficacy of homoeopathy for acute or chronic low back pain.
Herbal medicines
Some herbal remedies have reported efficacy compared with placebo (with low to moderate certainty) for both acute and chronic low back pain, such as cayenne or capsaicin plasters, devil’s claw, willow bark, and topical lavender oil.
However, the size of the effects is unclear due to critical heterogeneity across trials.
Evidence and practice
Despite limited supportive evidence, analgesics are still commonly used for low back pain.
In our experience, reasons for this include a real or perceived lack of alternatives, pressure from patients, a strong desire to help, and the lower cost and better accessibility of medicines compared with physical and psychological therapies.
If an analgesic is to be recommended for management of low back pain, oral NSAIDs (or topical NSAIDs if there are contraindications to oral formulations) probably have the most favourable benefit-harm balance. There is high to moderate certainty evidence that paracetamol, opioids, antidepressants, and anticonvulsants are not effective, and have associated harms.
Managing patients with low back pain
Despite lack of evidence for efficacy, many people with chronic low back pain are
already using long term analgesics, and forced tapering of analgesics with risk of withdrawal (opioids, anticonvulsants, and benzodiazepines) can cause harm
Some patients may require supportive treatments while undergoing tapering, and treatment for substance use disorders.
Some of the medicines used for low back pain carry the risk of drug interactions.
If analgesics are used, they should be at the lowest effective dose for the shortest duration, and as an adjunct to other non-medicine strategies that address the broader biopsychosocial aspects of pain.
Caitlin Jones, postdoctoral research associate, The University of Sydney Institute for Musculoskeletal Health; Martin Underwood, professor of primary care research, Warwick Medical School, Coventry, UK; Roger Chou, professor, Oregon Health & Science University, Portland, USA; Mark Schoene, patient representative, Cochrane Collaboration, Newbury, USA; Saniya Sabzwari, professor, Aga Khan University, Karachi, Pakistan; Jarrod Cavanagh, patient representative, Brisbane, Australia; Chung-Wei Christine Lin, professor, University of Sydney and Sydney Local Health District.
The BMJ article – Analgesia for non-specific low back pain (Open access)
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