While the popular painkiller has long been categorised as safe for pregnant women, a study tracking more than 7000 mothers and their babies in Britain reported an association between use of the drug during pregnancy and behavioural difficulties in children when they were aged seven.

It is the second such study to suggest a link between the two. A similar project tracking 64,000 Danish women and their babies reported a correlation between paracetamol use during pregnancy and ADHD-like behaviour in children at seven years of age. Some researchers have even questioned whether there could be a link between the drug and autism.

But Australian pharmacists urged women not to panic about the drug, saying the research has only pointed to an association for further investigation. They said there was no definitive proof the drug caused harm to fetuses.

The most recent study, published on Tuesday in the journal JAMA Pediatrics, said 7796 mothers were asked to report their use of paracetamol at 18 and 32 weeks into their pregnancy, and to report any behavioural problems in their children at the age of seven.

It found about 53 per cent of women took the drug at 18 weeks, and 42 per cent at 32 weeks.

When their children were seven, about 5 per cent of mothers said their children had behavioural problems, in a questionnaire that asked them about their child's interaction with peers, hyperactivity, and inattention among other things.

The researchers said that use of paracetamol at 18 weeks and 32 weeks was associated with an increased risk of behavioural problems. Use of the drug at 32 weeks was also associated with a higher risk of children having a range of emotional difficulties as well as behavioural problems.

The researchers said that given the widespread use of paracetamol among pregnant women, the study could have "important implications on public health advice".

But Dr Luke Grzeskowiak, a specialist pharmacist and researcher at the Robinson Institute and University of Adelaide, said while the study was interesting, it was not strong enough for pregnant women to stop using paracetamol if they needed it to relieve pain or fever.

Furthermore, he said although the study reported women using paracetamol during pregnancy had a 30 per cent increased relative risk of having a child with behavioural problems, this amounted to a very small actual risk.

"We're talking about an extra one to two cases [of behavioural problems] per 100 births being linked to paracetamol use," he said.

"So in this study, 95 per cent of mums who took paracetamol during pregnancy had a child with no problems at seven years of age … I think that message gets lost in a lot of this."

Dr Grzeskowiak said paracetamol was still the first choice of painkiller for pregnant women because others, such as anti-inflammatory drugs like ibuprofen (the active ingredient in Nurofen) had been linked to an increased risk of miscarriage during early in pregnancy, and harm to the fetus' kidneys and heart later in pregnancy.

"The key message from this study is only to take paracetamol when absolutely necessary and to take it for the shortest possible duration, not to avoid it completely," he said.