The researchers, led by Dr. Christopher Williams from the George Institute for Global Health at the University of Sydney, Australia, say their findings bring into question the "universal endorsement" of paracetamol as the main painkiller for low-back pain.
The new study compares paracetamol with a placebo and finds it is no better at aiding recovery and reducing short-term pain for low-back pain.
After conducting a systematic review of previous studies assessing the effectiveness of paracetamol for low-back pain, the team found no evidence to support its use. "All seven of the included trials had substantial methodological flaws, and only one trial included more than 25 participants per group," they write.
Additionally, they say no trial has compared paracetamol with a placebo or compared dosing.
As such, they conducted the Paracetamol for Low-Back Pain Study (PACE), which randomly assigned 1,652 participants, of an average age of 45 years, with low-back pain to receive regular doses of paracetamol for up to 4 weeks, paracetamol as needed (up to a maximum of 4,000 mg per day) or a placebo.
Regular dosing was considered as 3,990 mg per day. Additionally, all participants received advice and reassurance, and they were followed-up for 3 months.
Results showed that between the treatment groups, there were no differences in the number of days to recovery; the median time to recovery was 17 days for the regular paracetamol group, 17 days for the as-needed paracetamol group and 16 days for the placebo group.
The researchers also found that paracetamol did not have an effect on short-term pain levels, disability, function, sleep quality or quality of life.
'Paracetamol as first-line treatment for low-back pain should be reconsidered'
Commenting on their findings, Dr. Williams says paracetamol might not be the most important way to manage pain for acute low-back pain:
"The results suggest we need to reconsider the universal recommendation to provide paracetamol as a first-line treatment for low-back pain, although understanding why paracetamol works for other pain states but not low-back pain would help direct future treatments."
Though this latest study is the first large trial to compare the effects of paracetamol with placebo on low-back pain, in a linked comment, Bart Koes and Wendy Enthoven - from Erasmus MC, University Medical Center in Rotterdam, Netherlands - caution that more studies need to be conducted.
"Although the findings from this high-quality trial are clear," they write, "the content of guidelines should not be changed on the basis of a single trial; more robust and consistent evidence, including verification of the results in other populations, is needed."
And the researchers themselves note some limitations of the study. For example, participants did not typically take the full recommended paracetamol dose; the overall median intake was around 2,660 mg/day, so the authors add that the "accumulated response from regular dosing, equivalent to 4,000 mg/day, might have been more effective."
However, they also note that they did not observe any indication of effect on pain intensity during the first weeks of the trial when the median dose was close to the maximum, at 3,500 mg/day.
The study authors conclude their study by noting:
"In view of the quick timeframe in which participants in our trial improved across all the outcomes measured, compared with other cohorts, advice and reassurance (as provided in our trial) might be a more important aspect of medical care than pharmacological strategies for acute episodes of low-back pain."
In 2013, the Food and Drug Administration (FDA) warned that acetaminophen could cause serious skin reactions in rare cases.