Is paracetamol any good for treating flu?

“Paracetamol will not ease the symptoms of flu, according to a study by doctors in New Zealand,” The Times reports. 

A small study suggests the widely used painkiller does not help combat the overall effects of infection.

The trial specifically looked at whether paracetamol had any effect on the amount of flu virus in the body (viral load).

But it should be stressed this is something paracetamol is not designed to do. Paracetamol is designed to relieve symptoms, not cure any underlying infection.

Researchers randomly assigned 40 people to take paracetamol and 40 to take a dummy tablet. Over a period of five days, they recorded the patients’ viral load, as well as measuring their temperature and other flu symptoms.

Both groups were also given the anti-flu drug oseltamivir and additional pain relief when required. The study found no difference between the two groups for any outcome.

Paracetamol is a drug intended to treat fever and mild pain, not cure infection. Although the study did look at these outcomes as well, it was not set up to examine them and may have been too small to reliably detect differences between the groups.

The trial provides a route for further research, but with so many other studies reporting the opposite, it is too early to be changing recommendations.  

Where did the story come from?

The study was carried out by researchers from a number of institutions, including the Medical Research Institute of New Zealand and the department of medicine at the University of Otago, Wellington.

Funding for the study was provided by the New Zealand Health Research Council. 

It was published in the peer-reviewed medical journal Respirology on an open-access basis, so it is free to read online or download as a PDF.

The trial has been reported accurately by the media. The Mail Online rightly pointed out this is only the finding of one study – with so many other studies reporting the opposite, it is too soon to be changing official recommendations for treating flu.

Though its headline – “Paracetamol for flu? It’s pointless, say scientists: Popular drug neither reduces fever nor aches and pains” – implies there has been a change in a consensus of expert opinion, which is not the case.   

What kind of research was this?

This double-blind, randomised controlled trial aimed to investigate the effects of paracetamol on reducing the viral load and symptoms of flu.

This is the best design to address this question as any differences in patients’ characteristics should be balanced between groups, and any observed differences are more likely to be down to the treatment rather than other confounding effects.

However, the strength of the evidence these types of trials provide can vary widely, particularly if the trial is small (like this one) and when looking at outcomes other than the main one the study set out to examine. 

What did the research involve?

Potential participants were referred by doctors in the Wellington region of New Zealand if they met the following criteria:

• they were aged 18 to 65
• they had symptoms of a flu-like illness – a history of fever or a temperature over 37.8C
• they had at least one symptom of a cough, sore throat, runny nose, headache, muscle aches, fatigue or generally feeling unwell for less than 48 hours

People were excluded if:

• there was a need for hospital admission
• they regularly used paracetamol or non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, excluding low-dose aspirin

Those who tested positive for flu were eligible.

The 80 people who participated in the study were randomly assigned to receive paracetamol (1g) or a visually identical placebo (dummy) tablet four times a day for a period of five days – this was a 4g daily dose of paracetamol, which is the maximum allowed.

All participants received a five-day course of the anti-flu drug oseltamivir. If needed, they could also be given low-dose codeine for pain relief.

At baseline, demographic and clinical characteristics were recorded. This included whether the patients also had respiratory and cardiovascular problems, their ethnicity, if they had received the flu vaccination, and the strain of flu.

The main outcome the trial aimed to examine was flu viral load, which was measured at 24 hours (day one), 48 hours (day two) and 120 hours (day five).

Other outcomes examined included fever and other flu symptoms. These were self-rated by the participants, who gave a daily record from the start of the study until they got better or up to day 14, whichever came first.

They were asked to rate their health symptoms, ranging from “worst possible health” to “my health is normal for me”. 

What were the basic results?

The change for the viral load from baseline to day five was not significantly different between groups. There was also no difference for temperature (maximum or daily average), symptom score, or how long it took to get better and their health status.

Adherence to the assigned treatment was 100% in both groups for the initial 48 hours. This declined to 92.8% in the placebo group and 88.4% in the paracetamol group for the remaining three to five days.

There was no difference between the groups in the amount of codeine pain relief requested – an average of 30mg in both groups over the first 48 hours. 

How did the researchers interpret the results?

The researchers concluded that regularly taking paracetamol while ill with flu has no effect on viral load, temperature or clinical symptoms, and there is an insufficient evidence base for the use of paracetamol in treating flu infection. 

Conclusion

This double-blind, randomised controlled trial aimed to assess the effect of paracetamol on reducing viral load and clinical symptoms of flu.

The researchers found paracetamol had no effect on any outcome in people with flu – on viral load, temperature or clinical symptoms – and feel there is not enough evidence to provide the drug as a treatment.

However, there are a few points to bear in mind. The randomised design and double-blind nature of the trial are strengths, as these should reduce the risk of bias in how patients were allocated to groups, as well as the risk of bias in outcome reporting. 

Although efforts were made to account for risk, there was an imbalance in the number of participants with respiratory conditions and prior flu vaccination, which may have affected the results.

But probably the most important limitation is that this was a relatively small trial, which set out to examine the effect of paracetamol on viral load as its main outcome.

Paracetamol is a drug intended to treat fever and mild to moderate pain, not cure infection. For that, an antiviral drug would be required, but there is still a longstanding debate about how effective antivirals actually are.

While the trial did also examine paracetamol’s effect on symptoms, the study may have been too small to reliably detect differences between the groups for these symptom outcomes.

The researchers did provide calculations to show that their trial had a sufficient sample size to reliably detect differences in viral load, but there is no evidence to show it had sufficient “statistical  power” to test whether paracetamol was effective or not for the job it is actually designed to do.

The study also provides no evidence for the use of paracetamol in other infections or pain conditions.    

These findings are said to be the first to come from a randomised controlled trial, and provide a route for further research. However, because of this study’s limitations, and with so many other studies reporting the opposite findings, it is too early to be changing recommendations. 

Flu is usually managed at home – you will feel better within a week as long as you rest, keep warm and drink lots of water. Paracetamol may be a useful addition if you have a high temperature and the aches and pains associated with flu. Adults should take no more than 4g (usually eight 500mg tablets) of paracetamol in any 24-hour period.

You can prevent the spread of flu through good hygiene, including washing your hands carefully, and, for some people – the elderly or those with a weak immune system, for example – by having the seasonal flu vaccination.

Links To The Headlines

Paracetamol ‘doesn’t help to ease flu’. The Times, December 14 2015

Paracetamol for the flu ‘has no effect’, say scientists. The Daily Telegraph, December 13 2015

Paracetamol for flu? It’s pointless, say scientists: Popular drug neither reduces fever nor aches and pains. Mail Online, December 13 2015

Links To Science

Jefferies S, Braithwaite I, Walker S, et al. Randomized controlled trial of the effect of regular paracetamol on influenza infection. Respirology. Published online December 6 2015