(1) A finding by the commission approved laboratory of a prohibited drug, chemical or other substance in a test specimen of a horse is prima facie evidence that the prohibited drug, chemical or other substance was administered to the horse and, in the case of a post-race test, was present in the horse's body while it was participating in a race. Prohibited substances include:

(a) Drugs or medications for which no acceptable threshold concentration has been established;

(b) Therapeutic medications in excess of established threshold concentrations;

(c) Substances present in the horse in excess of concentrations at which such substances could occur naturally; and

(d) Substances foreign to a horse at concentrations that cause interference with testing procedures.

(2) Except as otherwise provided by this chapter, a person may not administer or cause to be administered to a horse by any means, a prohibited drug, medication, chemical or other substance, including any restricted medication pursuant to this chapter during the twenty-four hour period before post time for the race in which the horse is entered.