Acetaminophen - also known as paracetamol and marketed under brand names such as Mapap, Panadol and Tylenol - is not effective for the treatment of lower back pain and offers little value for osteoarthritis of the hip or knee, according to a study published in The BMJ.
The systematic review and meta-analysis is a synthesis of the research evidence from 13 randomized controlled trials designed to investigate the safety and efficacy of acetaminophen in the management of spinal pain - lower back or neck - and osteoarthritis.
The paper concludes that the widely used painkiller is ineffective against lower back pain and offers only "minimal short-term benefit" for people with osteoarthritis of the hip or knee.
The authors of the study call for updates to guidelines that currently recommend acetaminophen as the first analgesic option.
Lead author Gustavo Machado, of The George Institute for Global Health in the UK and the University of Sydney in Australia, says:
"Worldwide, paracetamol is the most widely used over-the-counter medicine for musculoskeletal conditions, so it is important to reconsider treatment recommendations given this new evidence."
Opinion leaders in the fields of general practice and rheumatology write in an editorial article about the study that some of its findings are not surprising.
Professors Christian Mallen and Elaine Hay say in the same issue of The BMJ that the new evidence reopens a debate that has already raised questions about the value of the painkiller. They cite, for example, the changing advice of the UK's drug-rationing body on the prescription of acetaminophen for osteoarthritis.
These questions leave "patients and clinicians wondering what is left that can help to manage these common, painful and highly disabling conditions."
The editorial urges physical treatments as the way forward, including exercise. It concludes:
"Ongoing and ever-increasing concerns about pharmacological management of musculoskeletal pain highlights the importance of nonpharmacological options, which form the cornerstone of self-management of spinal pain and osteoarthritis."
The review of the studies comparing acetaminophen against placebo found "high-quality" evidence that:
- The painkiller is ineffective in patients with low back pain for reducing pain intensity and disability
- The analgesic produces a significant but "clinically unimportant" effect on pain and disability in patients with osteoarthritis.
Similar conclusions were reached in a study published in The Lancet in July of 2014, that acetaminophen "does not ease low-back pain."
The authors of the present study also found that acetaminophen increased the likelihood of having abnormal results on liver function tests compared with placebo.
Machado explains: "Use of paracetamol for low back pain and osteoarthritis was also shown to be associated with higher risk of liver toxicity in patients." The clinical relevance of this, however - the way it affects patients - remains uncertain, say the authors.
Levels of overall adverse side effects across the studies were not found to be higher for the painkiller compared with placebo. However, acetaminophen, like any drug, is not 100% safe, and the evidence concerning this has developed recently.
Safety issues with acetaminophen
Prof. David Hunter, an osteoarthritis expert from the University of Sydney but not one of the authors, cites recent evidence to show that "paracetamol can be associated with an increasing incidence of mortality, and increased risk of cardiovascular, gastrointestinal and renal disease in the general adult population."
We reported earlier this month on the study Prof. Hunter refers to - it suggested the risks of acetaminophen have been underestimated.
Acetaminophen has been the subject of tighter controls from the US drug regulator the Food and Drug Administration (FDA) in recent years. Since 2013, new warnings have been included on labels because of the risk of rare but serious skin reactions.
More recently, the maximum dose of acetaminophen in any tablet or capsule that combines the drug with an opioid painkiller has been restricted to 325 mg. Since March 2014, no manufacturer has marketed the treatments with a dose above this. The FDA explains this latest safety control in this YouTube video.