David,
May I suggest you go to www.fda.gov and read the definitions of food and drug.  Then go to the FD&C Act and read the definitions.  Then go to our state laws 69.41.020
(10) "Drug" means:
(a) Substances recognized as drugs in the official United States pharmacopoeia, official homeopathic pharmacopoeia of the United States, or official national formulary, or any supplement to any of them;
(b) Substances intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease in human beings or animals;
(c) Substances (other than food, minerals or vitamins) intended to affect the structure or any function of the body of human beings or animals; and
(d) Substances intended for use as a component of any article specified in (a), (b), or (c) of this subsection. It does not include devices or their components, parts, or accessories."
Fluoride is recognized as a drug in each of USP, OHP, ONF of (a).