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 Sec. 382.107 of this part, 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.