Respiratory infections are likely to have an influential role, the findings suggest. And the evidence is simply not strong enough to warrant changes to current guidance on the use of this medicine, say the researchers.
The use of paracetamol during pregnancy and/or a child's early life has been implicated in the development of childhood asthma, prompting concerns to be raised about the drug's continued use during these periods.
The researchers wanted to find out if the available evidence was sufficient to rule out the role of common respiratory infections, which paracetamol is often used to treat, and which are themselves risk factors for the development of asthma.
They therefore trawled research databases for published evidence, spanning a period from 1967 to 2013. Out of the 1192 potentially relevant studies, 11 were suitable for inclusion in the analysis.
The seven studies covering the potential link between exposure to paracetamol while in the womb and subsequent childhood asthma reached widely varying conclusions, and only one took account of the potential role of respiratory infections during pregnancy.
Six of the studies looked at exposure to paracetamol during the first two years of life--a critical period for lung development.
Although these studies consistently pointed to a link between the drug and the development of asthma, the association was considerably weakened after respiratory tract infections during infancy had been accounted for.
And while a link was found between the number of times a child had been given paracetamol and that child's asthma risk, this link all but disappeared when respiratory tract infections were taken into consideration, "making it unlikely that paracetamol is a clinically important risk factor asthma," write the authors.
It remains unclear what role, if any, maternal respiratory infection during pregnancy might have, as only one study took this into account.
A proper trial looking at the influence of paracetamol on the development of asthma is highly unlikely as it would require some babies to be given a dummy pill, which many parents would not be willing to do, say the authors.
All in all, the current evidence for a link between the drug's use and the development of asthma is "weak," they say.
And they conclude: "The evidence of an association between early life paracetamol and asthma is often overstated, and there is currently insufficient evidence to support changing guidelines in the use of this medicine."