49 CFR 219.103 - Prescribed and over-the-counter drugs.
(a) This subpart does not prohibit the use of a controlled substance (on Schedules II through V of the controlled substance list) prescribed or authorized by a medical practitioner, or possession incident to such use, if -
(1) The treating medical practitioner or a physician designated by the railroad has made a good faith judgment, with notice of the employee's assigned duties and on the basis of the available medical history, that use of the substance by the employee at the prescribed or authorized dosage level is consistent with the safe performance of the employee's duties;
(2) The substance is used at the dosage prescribed or authorized; and
(3) In the event the employee is being treated by more than one medical practitioner, at least one treating medical practitioner has been informed of all medications authorized or prescribed and has determined that use of the medications is consistent with the safe performance of the employee's duties (and the employee has observed any restrictions imposed with respect to use of the medications in combination).