On Monday, President Donald Trump said that taking Tylenol (acetaminophen) while pregnant can cause autism in babies. His comments were quickly criticized, even by former President Barack Obama, who said they “undermined public health.”

Trump said that people who don’t get vaccines or take pills have “no autism,” and then he asked U.S. Health Secretary Robert F. Kennedy Jr. if what he said was true. He also said that the FDA would give doctors new advice, saying, “Ideally, you don’t take it at all, but if you have to, if you can’t tough it out, you’re going to end up doing it.”

The World Health Organization quickly responded, saying that there is “currently no conclusive scientific evidence confirming a possible link between autism and use of acetaminophen.” The WHO said that autism spectrum disorder (ASD) affects almost 62 million people around the world and is caused by a number of factors that are still not fully understood.

At an event in London, Obama talked about the controversy and told a crowd of 14,000 that Trump’s comments were “violence against the truth.” He said that these kinds of claims could hurt pregnant women, make parents scared, and slow down progress in understanding autism.

He also said that the rise in autism diagnoses is not necessarily a sign of more cases, but rather of better diagnostic criteria and more awareness. Obama said, “All of that is violence against the truth.”

The company that makes Tylenol put out its own statement, saying that the drug is “one of the most studied in history” and “safe when used as directed by expecting mothers, infants, and children.”

The company also said that more than ten years of research have not found any credible evidence linking acetaminophen to autism. It is still recommended as the first treatment for pain and fever by independent health authorities.

Tylenol reps also told pregnant women that having high fevers and pain that isn’t treated can be dangerous, especially in the first trimester. They told them to talk to their doctors.