Sweat it out (Image: Tom Merton/Plainpicture)

Leader: “Counting the hidden victims of medicine“

Next time you feel the flu coming on, think twice before reaching for painkillers – they could do more harm than good.

With the flu season under way across Europe and North America, millions will be taking flu remedies, which commonly include painkillers. The general medical advice in the UK and the US is to take painkillers such as paracetamol (acetaminophen) or aspirin. But although painkillers can make you feel better they also lower fever, which can make the virus worse.


The first analysis of the effect of this on the population shows that painkillers taken at current levels to treat fevers could cause 2000 flu deaths each year in the US alone.

Fever is thought to be an antiviral weapon, because many viruses find it hard to replicate above our normal 37 °C. But research hasn’t made it clear whether relieving fever slows recovery.

Some studies have shown that lowering fever may prolong viral infections and increase the amount of virus we can pass on to others, says David Earn at McMaster University in Hamilton, Canada.

To find out what impact this might have on a flu epidemic, Earn and his colleagues turned to a 1982 study which showed that ferrets, a common animal model for human flu, produced more seasonal flu virus if their fevers were lowered either with painkillers or by having their fur shaved off.

Earn’s team used these findings to estimate how much more virus people with ordinary flu might produce if their fevers were suppressed, and used epidemiological studies in people to estimate how many more cases of flu this might cause.

With the help of a mathematical model they applied these estimates to the number of people a year in the US who get flu, develop fever and take the drugs.

They found that painkillers as used in the US could be increasing the transmission of ordinary winter flu by up to 5 per cent.

Every winter 41,000 people on average, mostly elderly, die of flu in the US. So this could mean 700 to 2000 extra deaths per year, depending on the flu strain circulating.

Paul Andrews, a member of the McMaster team, says their estimate is conservative because it factors in only increased amounts of virus shed. Longer shedding time would also make a difference, as would people who feel better with painkillers returning to work or school while still infectious.

Others are more cautious. Nick Phin, head of respiratory diseases at Public Health England, thinks the study relies too much on animal data. He says painkillers are safe and effective against flu.

It is best to avoid using these drugs routinely, however, says Edward Purssell of King’s College London. He was on an official panel in England last year that recommended painkillers in children under 5 only to relieve pain. “Fever won’t hurt,” he says, “and it might help”.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2013.2570

This article will appear in print under the headline “A touch of flu? Hold the painkillers”