O.C.G.A. § 20-2-1120

As used in this part the term “illegal drugs” shall include marijuana as defined in paragraph (16) of Code Section 16-13-21, a controlled substance as defined in paragraph (4) of Code Section 16-13-21, a dangerous drug as defined in Code Section 16-13-71, or any other controlled substance or dangerous drug that persons are prohibited by state or federal law from using, but shall not include any drug when used pursuant to a valid medical prescription or when used as otherwise authorized by state or federal law.