Paracetamol is the first-line treatment for GPs dealing with acute attacks of the most common form of back pain, while the NHS Choices websites advises patients to take it.
But a major trial shows the painkiller does not help sufferers recover more quickly, reduce their pain levels or improve their sleep or quality of life.
The research suggests advice and reassurance can do as much good for back pain patients as regular doses of paracetamol.
This could include advising patients to rest and to improve their posture and reassuring them that they will get better.
Lower back pain is thought to affect two in five people at some point in their lives, being triggered by bad posture, bending awkwardly or lifting incorrectly. In many cases it gets better within 12 weeks, with sufferers taking painkillers and keeping mobile.
Despite universal advice to doctors about prescribing paracetamol to alleviate low back pain, there is no high-quality evidence which shows it works, according to Australian researchers.
They carried out their study on 1,652 people with acute lower back pain in Sydney. The volunteers, who had an average age of 45, were split into three groups.
One group received regular doses of paracetamol three times a day for up to four weeks. They were given up to 3,990mg per day.
Another group received up to 4,000mg of paracetamol per day when required, and the third were given a placebo (dummy pills).
The study found little difference in the number of days it took to recover between the treatment groups, with the placebo group having an average recovery time of 16 days, a day faster than the other two groups. Paracetamol also had no effect on short-term pain levels, disability, function, sleep quality or quality of life, says to a report in The Lancet medical journal.
According to study leader Dr Christopher Williams, from Sydney University, paracetamol was effective in treating some acute pain such as tooth extraction and post-operative pain.
But the study findings threw into doubt its role in treating low back pain. ‘Simple analgesics such as paracetamol might not be of primary importance in the management of acute lower back pain,’ he said.
‘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.
In view of the quick time frame in which participants in our trial improved compared with other cohorts, it would be interesting to see whether advice and reassurance, as provided in our trial, might be more effective than pharmacological strategies for acute low back pain.’
But Dutch experts Bart Koes and Wendy Enthoven, from Erasmus University Medical Centre in Rotterdam, also writing in The Lancet, said it was too early to change clinical guidelines.
They said: ‘Although the findings from this high-quality trial are clear, 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.’
Paracetamol works by blocking prostaglandin enzymes in the brain and spinal cord involved in the transmission of pain.
In addition to paracetamol tablets, the drug is available in many cold and flu remedies. In 2011 the NHS spent £61million on paracetamol for GPs’ patients.