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Some asthma experts are urging greater caution in the use of paracetamol, after an international study of more than 200,000 children suggested the painkiller increased the risk of the breathing complaint.
But the Ministry of Health says people should not stop using the over-the-counter medicine on the strength of the study, which asked the parents about previous paracetamol use by their children aged 6 or 7.
Paracetamol's increasing use internationally has paralleled the rising prevalence of asthma. In New Zealand, where it is the most widely used medicine, around a quarter of children and a sixth of adults have asthma.
The study, involving four New Zealand authors and published in Britain's Lancet medical journal, found using paracetamol at least monthly in the preceding year increased the risk of asthma three-fold.
Smaller but still notable increases in asthma risk were found:
* In children who had used the drug at least once in the preceding year. * In those who had been given paracetamol for fever in the first year of life.
The study also linked paracetamol to increased risk of hay fever and eczema.
No one knows for certain what causes asthma and the paracetamol theory, and others, have been under investigation for some years.
This kind of study can only suggest, not prove, cause and effect. But the fact that an increasing dose in the preceding year was associated with a greater risk of asthma was said by the authors to be one of several factors indicating paracetamol could be a causal factor.
The Asthma and Respiratory Foundation's medical director, Professor Robin Taylor, said paracetamol should continue to be used for babies, especially if a high fever posed a threat of dehydration or convulsions.
Asthma New Zealand's medical director, Dr Allen Liang, said parents tended to overuse paracetamol with babies who were teething or had a mild fever.
An increased temperature helped the body to fight infection and in children should be treated with paracetamol only above 38.5C.
The ministry said it would assess all evidence linking asthma to paracetamol but because the study did not prove cause and effect, the drug "should continue to be used as directed until clearer information is available".
Aspirin should be avoided in children because of the risk of developing Reye's syndrome, a rare disorder which causes brain and liver damage.
