What the evidence tells us about Tylenol, leucovorin, and autism

Could Tylenol, one of the most ubiquitous medicines in the U.S., be linked to some cases of autism spectrum disorder when taken during pregnancy? And could leucovorin, a form of folic acid, improve the verbal ability of some people with autism spectrum disorder?

Those are two possibilities that President Trump and Robert F. Kennedy Jr., the secretary of health and human services, seized on Monday in an announcement at the White House. Neither is new; data suggesting that Tylenol use in pregnancy could increase the risk of an infant developing autism and that leucovorin may help some patients have circulated for more than a decade. But in both cases it is exceedingly difficult to tease out verifiable risks and benefits from hypotheses alone.

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