On Friday, the United States Food and Drug Administration, or FDA, said it will limit fluoride pills and drops for children.
The new rule stops companies from selling these drugs for kids under 3 years old and for older children who have low risk of tooth decay.
Doctors and dentists can still give fluoride medicine to children who really need it.
Fluoride is a mineral found in some water and food.
It makes tooth enamel stronger and helps stop tooth decay.
Many towns add fluoride to public water to help everyone protect their teeth.
Some new studies say too much fluoride might hurt a child's gut microbiome and even lower IQ.
The FDA says more research is needed, so it wants to be careful.
Dentists say fluoride is safe and helpful when used in the right amount.
In places with no fluoride in public water, they still advise starting fluoride pills at 6 months of age.