(a) This chapter does not apply to the sale of any product dispensed or delivered by a pharmacist according to a prescription issued by a practitioner for a valid medical purpose within the scope of the practitioner's practice as authorized by the practitioner's license issued under Title 3, Occupations Code.
(b) This chapter does not require a business establishment to:
(1) keep specific records of transactions covered by this chapter; or
(2) store dextromethorphan in a specific location in a business establishment or otherwise restrict the availability of dextromethorphan to customers.