Two recently published studies have linked regular use of acetaminophen in adults and children to a significantly increased risk of developing asthma.

In the first study, Dr Seif Shaheen and colleagues from institutes across Europe found that asthmatic adults were 2.5 to 2.9 times more likely to have taken acetaminophen regularly (at least once weekly as opposed to less than weekly) than controls. No association was found between asthma and use of other painkillers. The researchers conclude that their findings demonstrate a positive association between the frequent use of acetaminophen and adult asthma.

For the second study, Professor Richard Beasley and colleagues looked at data obtained from 205,487 children aged between 6 and 7 years old from 31 countries, making it the largest study to date examining the relationship between acetaminophen use and childhood asthma. Results showed that use of acetaminophen for fever in the first year of life was associated with a 46% increased risk of asthma by the age of six or seven. Acetaminophen use, both in the first year of life and in children aged 6-7 years, was also associated with an increased risk of symptoms of rhinoconjunctivitis and eczema. The authors conclude: "We suggest that exposure to paracetamol  [acetaminophen] might be a risk-factor for the development of asthma in childhood. We stress the findings do not constitute a reason to stop using paracetamol in childhood. Paracetamol remains the preferred drug to relieve pain and fever in children. However the findings do lend support to the current guidelines of the World Health Organisation, which recommend that paracetamol should not be used routinely, but should be reserved for children with a high fever (38.5Ëš C or above)."

Shaheen S, Potts J, Gnatiuc L, Kowalski ML, Joos G, van Zele T, et al. The relation between paracetamol use and asthma: a GA2LEN European case-control study. Eur Respir J. Published online before print June 25, 2008. doi:doi:10.1183/09031936.00039208.

Beasley R, Clayton T, Crane J, von Mutius E, Lai CKW, Montefort S, Stewart A, for the ISAAC Phase Three Study Group. Association between paracetamol use in infancy and childhood, and risk of asthma, rhinoconjunctivitis, and eczema in children aged 6–7 years: analysis from Phase Three of the ISAAC programme. The Lancet. 2008;372:1039-1048.