Dynamic Chiropractic Canada – May 1, 2015, Vol. 08, Issue 05

A Poor Choice for Pain Relief

Acetaminophen ineffective for short-term relief of LBP, knee / hip OA pain.

By Peter W. Crownfield, Executive Editor

Acetaminophen is the most popular pain reliever in the U.S., accounting for an estimated 27 billion annual doses as of 2009. With 100,000-plus hospital visits a year by users, it's also the most likely to be taken inappropriately. In fact, improper use, coupled with the drug's narrow safety margin, means "a large fraction of users [are] close to a toxic dose in the ordinary course of use," according to the Food and Drug Administration.

But for the sake of discussion, let's ignore the safety issues for a moment. Is acetaminophen an effective pain reliever in the first place? Not for low back pain and pain attributable to knee / hip osteoarthritis, conclude the authors of a recent meta-analysis. The just-published review of 13 randomized trials has yielded "high-quality evidence" that paracetamol (acetaminophen) does not reduce pain intensity or disability, and does not improve quality of life, in the short term for people experiencing LBP; and provides only "minimal, short-term benefit" for people suffering from hip or knee pain caused by OA, stating that "the small effects ... are not likely to be meaningful for clinicians or patients."

Back to the safety issues surrounding acetaminophen, which the meta-analysis did little to dilute. According to the review researchers, "high-quality" evidence suggests paracetamol use results in a fourfold risk of an abnormal liver function test. Not surprising, since acetaminophen misuse (overdose) is now the most common cause of acute liver failure (exceeding all other medications combined) and the second most common cause of liver failure requiring transplantation.

poor choice - Copyright – Stock Photo / Register Mark In fact, the FDA has mandated that all acetaminophen-containing prescription products feature a "black box" warning (the administration's strongest safety statement) noting an overdose can cause liver failure and even death; and have been urged to place similar language on OTC acetaminophen products.

Assessing the Evidence

The review researchers performed a systematic electronic search in Medline, Embase, AMED, CINAHL, Web of Science, LILACS, International Pharmaceutical Abstracts, and Cochrane Central Register of Controlled Trials up to December 2014, selecting only randomized, controlled trials comparing paracetamol to placebo for nonspecific spinal pain (neck or LBP), or osteoarthritis of the hip or knee. Trials eligible for inclusion also had to report on one or more of these primary outcome measures: pain intensity, disability status and quality of life. (Secondary outcome measures included adverse effects, patient compliance and use of rescue meds.)

Overall, 13 studies met inclusion criteria and served as the basis for the analysis. Three trials consisting of 1,825 patients evaluated paracetamol for LBP; 10 trials evaluated efficacy for patients (3,541) with hip or knee OA.

In the reviewed studies, paracetamol was primarily administered orally (as tablets / capsules); one study evaluated intravenous paracetamol use by participants with chronic LBP. Total oral dose and dose regimens varied (3,900-4,000 mg/day in 10 trials; 3,000 mg/day in three trials).

After analyzing the eligible study pool, the reviewers even performed "a post-hoc analysis to assess the effect of a new trial in our meta-analysis," which only served to confirm their original findings: "The results of a new trial added to current evidence would not change the conclusion that paracetamol does not deliver a clinically important benefit (at least 9 points out of a 0-100 range) for spinal pain and osteoarthritis."

Clinical Applications

What percentage of your existing patient base uses acetaminophen-containing OTC and/or prescription medications for their LBP and OA pain, even as they pursue relief through chiropractic care? If you don't know, it's time to find out. Now imagine how many current non-patients take these drugs for their spinal / OA pain instead of visiting your office. As this meta-analysis suggests, acetaminophen is ineffective for these types of pain. What an opportunity for chiropractic to become the primary conservative pain-relief option. The research-backed result for your patients (and soon-to-be patients): less medication (mis)use and more pain relief.


  • Machado GC, et al. Efficacy and safety of paracetamol for spinal pain and osteoarthritis: systematic review and meta-analysis of randomised, placebo-controlled trials. Brit Med J, 2015;350. Full text available online.
  • Dal Pan GJ. "Acetaminophen: Background and Overview." FDA Office of Surveillance and Epidemiology, Center for Drug Evaluation and Research, June 29, 2009.
  • Greenlaw E. "Your Guide to Over-the Counter Pain Relief. OTC Pain Relief: Understanding Acetaminophen." WebMD.com.
  • Healy M. "Acetaminophen in Rx Drugs: For Liver's Sake, Lower the Dose." Los Angeles Times, April 28, 2014.
  • Gerth J, Miller TC. "Use Only as Directed." ProPublica, Sept. 20, 2013.

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