49 CFR §392.4

1. (a)No driver shall be on duty and possess, be under the influence of, or use, any of the following drugs or other substances:
   1. (1)Any 21 CFR 1308.11 Schedule I substance;
   2. (2)An amphetamine or any formulation thereof (including, but not limited, to “pep pills,” and “bennies”);
   3. (3)A narcotic drug or any derivative thereof; or
   4. (4)Any other substance, to a degree which renders the driver incapable of safely operating a motor vehicle.
2. (b)No motor carrier shall require or permit a driver to violate paragraph (a) of this section.
3. (c)Paragraphs (a) (2), (3), and (4) do not apply to the possession or use of a substance administered to a driver by or under the instructions of a licensed medical practitioner, as defined in § 382.107 of this subchapter, who has advised the driver that the substance will not affect the driver's ability to safely operate a motor vehicle.
4. (d)As used in this section, “possession” does not include possession of a substance which is manifested and transported as part of a shipment.