§ 102-74.400 What is the policy concerning the possession and use of narcotics and other drugs?
Except in cases where the drug is being used as prescribed for a patient by a licensed physician, all persons entering in or on Federal property are prohibited from—
(a) Being under the influence, using or possessing any narcotic drugs, hallucinogens, marijuana, barbiturates, or amphetamines; or
(b) Operating a motor vehicle on the property while under the influence of alcoholic beverages, narcotic drugs, hallucinogens, marijuana, barbiturates, or amphetamines.
https://www.ecfr.gov/current/title-41/subtitle-C/chapter-102/subchapter-C/part-102-74/subpart-C
You left out paragraph (c) except if you are __________________ . /s