S.C. Code Regs. 38-382.213. Controlled substances use

(a) No driver shall report for duty or remain on duty requiring the performance of safety-sensitive functions when the driver uses any controlled substance, except when the use is pursuant to the instructions of a licensed medical practitioner, as defined in Regulation 38-382.107, who has advised the driver that the substance will not adversely affect the driver's ability to safely operate a commercial motor vehicle. (b) No employer having actual knowledge that a driver has used a controlled substance shall permit the driver to perform or continue to perform a safety-sensitive function. (c) An employer may require a driver to inform the employer of any therapeutic drug use.