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Nov. 5, 2009 -- The popular pain and fever reliever acetaminophen may be linked with an increased risk of asthma in children and adults, according to a new research review of previously published studies by Canadian researchers.
But the manufacturer of Tylenol -- the brand-name version of acetaminophen -- says the painkiller has a well-established safety record.
Researchers pooled the results of 19 clinical studies, with a total of more than 425,000 participants, to see if the association between the pain reliever use and asthma (and wheezing in children) held up. It did.
What triggered the review? "Concern over the risk of acetaminophen and asthma highlighted by the 2008 ISAAC study, published in The Lancet," says the review's lead author Mahyar Etminan, PharmD, a scientist at the Vancouver Coastal Health Research Institute in British Columbia and an assistant professor of medicine at the University of British Columbia.
In the ISAAC (International Study of Asthma and Allergies in Childhood) study, researchers looked at more than 205,000 children, ages 6 to 7, in 31 countries and found that acetaminophen use for fever in the first year of life was linked to increased risk of asthma symptoms in children 6 to 7 years old. Current use of acetaminophen was also linked to increased risk of asthma symptoms.
Other studies, Etminan says, have produced conflicting results, so the Canadian team conducted the review.
Sales of acetaminophen products in the U.S. are about $1 billion annually, the researchers estimate.
Etminan's team searched the medical literature to find high-quality published studies, trying to quantify the risk of asthma and wheezing among acetaminophen users, as well as the effect of prenatal exposure to the medicine.
After eliminating studies that weren't scientifically sound enough, the researchers focused on 19 studies. Overall, they found that acetaminophen users were 63% more likely to have asthma than nonusers. Other findings:
The researchers concede that children with severe asthma may be more likely to get acetaminophen for viral or other infections that may actually be due to asthma or may precede an asthma diagnosis.
The finding of acetaminophen use and asthma is an association, they say, but not necessarily a cause and effect.
The researchers say other mechanisms may explain the link. Acetaminophen, they say, may boost an enzyme involved in the anti-inflammatory response in asthma.
There are other possible mechanisms. ''There isn't enough evidence to favor one over the other," Etminan says. He says more studies are needed to fully understand the association.