It inhibits important enzymes. Fluoride is more toxic than lead. There is enough fluoride in an ordinary tube of toothpaste to kill a small child. Fluoride adversely affects the central nervous system, causing behavioral changes and cognitive deficits. These effects are observed at fluoride doses that some people in fluoridated areas actually receive.
Some adults are hypersensitive to even small quantities of fluoride.
A recent epidemiology study shows a correlation between decreasing annual fertility rate in humans and increasing levels of fluoride in drinking water. Fluoride is not an essential nutrient. Fluoride was widely used as a rat poison until recently. Alternative tooth protection is available, e.g., better dental hygiene and diet, sealants. Ireland is the only democracy on Earth that forces fluoride on all its citizens by law.