WASHINGTON (AP) — On Friday, the U.S. Food and Drug Administration took steps to curtail the use of fluoride supplements intended to bolster dental health in children. This decision marks the latest initiative by Health Secretary Robert F. Kennedy Jr. and his team, challenging a chemical long regarded as a staple in oral care.

The FDA’s new guidelines no longer endorse these supplements for children under three years old, nor for older children who don’t have significant risks of cavities. Previously, such supplements were prescribed to children as young as six months old.

While the FDA had hinted in May that it might seek to completely remove these supplements from the market, Friday’s action fell short of that. Instead, the agency issued warning letters to four companies, instructing them to comply with the revised usage guidelines.

Fluoride tablets and lozenges are often recommended for young individuals at heightened risk of dental decay due to insufficient fluoride levels in their local water supply. Additionally, some companies offer fluoride drops for infants.

Accompanying this regulatory update, the FDA presented a new scientific review. The analysis suggests that fluoride supplements have limited effectiveness in enhancing dental health in children and may pose potential safety concerns, including digestive issues, weight changes, and effects on cognitive development.

“For the same reason fluoride may work to kill bacteria on teeth, it may also alter the gut microbiome, which may have broader health implications,” the agency said in a statement.

The agency also sent a form letter to dentists and other health providers warning about the risks of the products.

Those claims have been disputed by the American Dental Association, which has said there are no significant health problems associated with fluoride when used at the levels prescribed by dentists. The supplements can cause spotting or discoloration of teeth due to the extra fluoride, a downside the FDA also noted.

Dentists have warned that restricting fluoride supplements may result in more cavities and dental problems in rural communities, which are less likely to have fluoridated water. Kennedy is also seeking to end the practice of adding fluoride to drinking water throughout the U.S.

Fluoride strengthens teeth and reduces cavities by replacing minerals lost during normal wear and tear, according to the Centers for Disease Control and Prevention. In 1962, the agency set guidelines for how much should be added to water.

Kennedy, a former environmental lawyer, has called fluoride a “dangerous neurotoxin” tied to a range of health dangers.

The FDA regulates most dental products, including fluoride-containing toothpastes, supplements, mouthwashes and rinses. The agency’s actions don’t affect toothpastes, mouthwash or fluoride treatments used by adults or those offered in dentists’ offices.

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