President Donald Trump has linked autism to the use of popular pain medication Tylenol, elevating a claim not backed by scientific evidence to the forefront of US health policy.

In an extraordinary news conference at the White House, the Republican president delivered medical advice to pregnant women and parents of young children, repeatedly telling them not to use or administer the over-the-counter pain killer.

Trump also suggested leucovorin , a form of folic acid, as a treatment for autism symptoms.

The advice from Trump, who has no medical training and also pointed out "I'm not a doctor," goes against that of medical societies, which cite data from numerous studies showing acetaminophen plays a safe role in the well-being of pregnant women.

The Food and Drug Administration said

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