(1) For the purpose of this chapter, in addition to the substances in RCW 69.43.010, a precursor substance is any of the following substances or their salts or isomers:

(a) Gamma-butyrolactone (GBL); and

(b) Hydriodic acid.

(2) A precursor substance defined in subsection (1) of this section does not include any drug that contains ephedrine, phenylpropanolamine, or pseudoephedrine or any cosmetic if that drug or cosmetic can be lawfully sold, transferred, or furnished over-the-counter without a prescription or by a prescription under chapter 69.04 or 69.41 RCW.