There is no clear link between pregnant women taking the common painkiller acetaminophen and autism in their children, despite repeated claims otherwise by Donald Trump, according to the most comprehensive review of the existing evidence published Monday.

In September, the US president sparked outrage among the medical community by claiming that acetaminophen – also known as paracetamol – was associated with higher rates of autism.

Trump urged pregnant women to "tough it out" rather than take acetaminophen, comments which health researchers warned could scare women off their safest option to treat pain – and risked further stigmatizing autistic people.

The World Health Organization has emphasised that there is no robust evidence showing that acetaminophen – which is the main ingredient in massively popular painkillers such as Tylenol and Panadol – causes autism.

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On Monday, an "umbrella" review of all the scientific research yet conducted on the subject was published in the British medical journal BMJ.

"Existing evidence does not show a clear link between in utero exposure to acetaminophen and autism and ADHD in offspring," the UK-led team of researchers wrote in the review.

There have been several previous studies that suggested a possible link between acetaminophen and autism or attention deficit hyperactivity disorder (ADHD).

However, the quality of those studies was "low to critically low," the review said, partly because they did not take adequate steps to rule out potentially misleading factors such as whether autism runs in the family.

These controversial previous studies also could not establish exactly how acetaminophen might cause autism.

The umbrella review called for better research, pointing out that there has been a "historical and ongoing underinvestment in women's health research."

Beyond the Tylenol issue, Trump and his vaccine-sceptic Health Secretary Robert F. Kennedy Jr have repeatedly made unfounded claims about autism, including that there is an "epidemic" of cases.

However, experts maintain that the recent increase in autism rates is due to improved, broadened diagnosis methods along with growing awareness.