The FDA has defined a drug as “A substance intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease. A substance (other than food) intended to affect the structure or any function of the body.” It might seem like nutrients get a pass here but in fact descriptions of their effects often are interpreted as falling under the definition of the first sentence.
Implicit in the definition of a drug is that it treats abnormal function, restores normal function. If your horse has an infection and you give antibiotics, you correct the disease by killing the cause, the bacteria. However, very few drugs actually treat disease. Instead, they treat symptoms. The symptoms of a disease are caused by the body, not something that happens to it. Fever for example is a result of the immune system functioning normally. When you block a symptom with a drug, you are interfering with the body, not restoring it to normal function.
It has been suggested that when you megadose (any dose above the minimum required to prevent deficiency states is considered a megadose), the nutrient is actually working like a drug. At the far extreme, e.g. Selenium overdosing, with toxic doses, that may be true. However, responses at less than toxic doses are not necessarily having drug effects.
An example is vitamin E treatment for equine motor neuron disease (EMND). Equine motor neuron disease is a degenerative condition of the nervous system similar to Lou Gehrig’s disease. Vitamin E levels are very low in these horses and EMND was thought to be a vitamin E deficiency for a long time, but it has now been found even in horses that are on pasture, which rules out inadequate intake since fresh grass is a very rich source of vitamin E.
The progression of EMND can be stopped, symptoms of severe muscle wasting and gait changes sometimes even reversed, with high doses of vitamin E, 5000 to 10,000 IU/day.
The search goes on for the real cause of EMND, but an environmental toxin with oxidant effects in the central nervous system is a pretty safe bet. Again, I would not consider the action of vitamin E in these cases to be drug-like. There is simply a higher requirement for this key nervous system antioxidant because of the toxin. The higher dose is providing the body with the material it needs to function normally and protect itself from a challenge.
Despite the obvious connection between vitamin E and EMND, and the fact there is no other treatment, companies are not permitted to talk about specific vitamin E related diseases like EMND in materials describing vitamin E supplements because it is considered a drug claim. Does this make sense?
Eleanor Kellon, VMD