President Donald Trump issued the warning on Monday as the US drug regulator announced plans to add a label to paracetamol warning of an increased risk of autism and ADHD in children.

“Don’t take Tylenol. Don’t take it,” Trump said during a news conference at the White House while flanked by top public health officials.

“Fight like hell not to take it,” Trump said.

“There may be a point where you have to, and that you’ll have to work out with yourself.”

Trump also cast doubt on the medical consensus on childhood vaccines, suggesting that inoculations for measles, mumps and rubella should be administered separately instead of in the combined MMR shot.

“This is based on what I feel. The mumps, measles – the three should be taken separately,” Trump said.

“And it seems to be that when you mix them, there could be a problem.”

Trump’s comments drew condemnation from medical bodies, including the American Academy of Pediatrics and the American College of Obstetrics and Gynecology (ACOG), which have long recommended paracetamol as one of the few painkillers that is safe for women during pregnancy.

Half of pregnant women worldwide are estimated to take paracetamol – which is sold in different countries under brand names including Dyman, Panadol and Panamax – for pain relief and to reduce fevers, which can be potentially dangerous to both the foetus and the expectant mother.

ACOG president Steven J Fleischman called the suggestions of a link between paracetamol and autism “irresponsible”.

“When considering the use of medication in pregnancy, it’s important to consider all potential risks along with any benefits,” Fleischman said in a statement.

“The data from numerous studies have shown that acetaminophen plays an important – and safe – role in the well-being of pregnant women,” Fleischman said, using the name for paracetamol in the US.

While some research has found evidence of an association between paracetamol and neurological conditions such as autism, medical experts have cautioned that more robust studies have found no link, and that causation remains unproven.

One of the biggest population-based studies, published by Swedish researchers last year in The Journal of the American Medical Association, found no link when comparing children who had been exposed to the painkiller with siblings who had not.

Arthur Caplan, a bioethicist at the NYU Grossman School of Medicine, described the Trump administration’s moves as “hugely negative” for public health.

“The big reveal about autism was a total bust full of misinformation, a lack of evidence, bad advice and a bogus answer about the cause,” Caplan told Al Jazeera.

“I think mainstream medicine will ignore what he said today,” Caplan said.

“I think patients can’t trust federal science in the USA and must turn to other reputable sources.”

Catherine Lord, a professor of psychiatry at UCLA who specializes in autism, said studies showing a link between paracetamol use and autism were limited by the presence of confounding factors that are difficult to control for.

“I think the medical community will be firm that Tylenol in pregnancy does not cause autism, but will probably tell pregnant women they should always be careful about medication,” Lord told Al Jazeera.

“But they also need to realize that having a high fever or being in pain is not good for a growing baby either, so they should consult their doctor.”

In its updated guidelines announced on Monday, the US Food and Drug Administration cited evidence of a “correlation” between paracetamol use and autism, and noted studies suggesting a heightened risk when the drug is taken “chronically” throughout pregnancy.

Still, the drug regulator was notably less emphatic than Trump, noting that a causal relationship had yet to be established, and the existence of “contrary studies in the scientific literature”.

“It is also noted that acetaminophen is the only over-the-counter drug approved for use to treat fevers during pregnancy, and high fevers in pregnant women can pose a risk to their children,” the regulator said, using the other generic name for paracetamol.

Autism has no known single cause, but is believed to be related to an interplay of genetic and environmental factors, according to the American Academy of Pediatrics. (Al Jazeera)