Review raises questions about paracetamol as a common pain reliever

Paracetamol is sold as a leading brand medication globally for mild-to-moderate pain relief but a wide-ranging review of existing studies led by the University of Sydney shows it is unknown how well the over-the-counter pain reliever works for the majority of conditions for which it is taken.

Most reviews to date (22 out of 36 in this systematic review) only evaluated single doses of the pain reliever, whereas it is common for consumers to take numerous doses in a course of self-treatment.

“This means there is a gap in our knowledge as to how effective the commonly taken pain reliever is for a range of pain conditions,” said co-lead author Dr Christina Abdel Shaheed.

This new systematic review found evidence of effectiveness for just four conditions - including general headaches - but found it was ineffective for low back pain despite its popularity for common musculoskeletal conditions.

The review also highlights that the widely held view of paracetamol as safe may be based on short-term use at the recommended dosage and suggests that pain is best treated holistically.

The review was published today in the Medical Journal of Australia in addition to a companion feature in MJA Insight+.

Key findings:

• Paracetamol only had evidence of effectiveness as a pain reliever for four conditions studied: knee or hip osteoarthritis; (general, not migrane) tension headache; perineal pain after childbirth (between the anus and genital area); and craniotomy (removal of part of the skull); the effect for these conditions was modest.
• The evidence for lower back pain is that it provides no better outcomes than placebo; however, the healing effect of time could be mistaken for medicine efficacy.
• For the remaining conditions e.g. abdominal pain, pain during dental procedures, migraines and middle ear infection, it was unclear whether paracetamol relieved pain.
• Most studies that have been done to date were just for single-dose (taken on one occasion only i.e 1-2 tablets), whereas paracetamol is commonly taken more than once to treat a symptom.

Paracetamol is listed on the World Health Organisation’s 2017 List of Essential Medicines and is deemed “essential for addressing the most important public health needs globally”. It is commonly used to treat muscle or joint pain, pain from injury or surgery, headache, general body aches or cancer-related pain and is a very common treatment for chronic, or persistent, pain.

The study did not look at the use of paracetamol for lowering temperature.

Lead authors Dr Christina Abdel Shaheed and Dr Giovanni Ferreira from the Institute for Musculoskeletal Health at the University of Sydney Faculty of Medicine and Health said that given the widespread use for pain relief, the Australian researchers reviewed all overviews of clinical trials testing paracetamol’s ability to relieve pain. This systematic review included 36 reviews (more than 19,000 participants) across 44 pain conditions.

“This review for the first time brings together all the existing evidence about the efficacy of paracetamol to treat pain in one document,” said Dr Abdel Shaheed, from the School of Public Health.  

“For tension headache we know paracetamol works better than placebo - but for most other conditions we simply lack the evidence to be able to make strong or definitive statements about paracetamol’s effectiveness,” she said.

Dr Giovanni Ferreira added: “What is clear is that paracetamol does not effectively relieve back pain or most types of osteoarthritis, urging research into strategies that will help people experiencing musculoskeletal pain.”

The senior author and director of the Institute, Professor Chris Maher, said it was easy to mistakenly attribute pain relief with the use of paracetamol.

“From research we know the biggest contributor to the improvement in low back pain is probably natural history; in other words, back pain often gets better by itself. Even with a chronic condition like osteoarthritis it does fluctuate and if you seek care when it is bad, it is likely to improve anyway; this is precisely why we need controlled trials,” he said.

Co-author Professor Andrew McLachlan, Dean of Sydney Pharmacy School, said the review underscored the limits of the focus on single-dose trials, to explore efficacy in reducing the intensity of different types of short-term painful conditions.

“Single-dose study designs provide little help in understanding the possible effects of paracetamol in people with ongoing painful conditions and using paracetamol regularly for pain control,” he said.

Dr Abdel Shaheed concluded that people should not be relying on pain medicines as a standalone treatment for pain relief.

“Any pain medicine should be considered as part of a holistic care plan, alongside strategies such as exercise, physiotherapy, or other lifestyle changes. A conversation with the doctor or pharmacist can be a good way to help people know what alternatives, subsidised or not, are available for them,” Dr Abdel Shaheed said.

About paracetamol:

• Stick within the safe limits for using paracetamol (maximum 4 g daily for adults, which will vary depending on the formulation used).
• Bear in mind there are different types of paracetamol products (long-acting, which is generally higher dose, versus short-acting, i.e. 500 mg standard tablets in Australia); and cold and flu preparations (including decongestant) and popular over-the-counter products for pain relief (including ibuprofen) can also contain paracetamol.
• Do not use paracetamol for more than a few days at a time unless specifically advised to by a doctor or pharmacist.
• Consider combining the medicine with other non-drug strategies to optimise pain relief.

Declaration: Co-authors Christopher Maher, Richard Day, Andrew McLachlan, Christine Lin, and Jane Latimer were investigators in the PACE study (paracetamol for acute lower back pain), funded by the NHMRC and GlaxoSmithKline Australia.