21 C.F.R. § 201.120
A drug prepared, packaged, and primarily sold as a prescription chemical or other component for use by registered pharmacists in compounding prescriptions or for dispensing in dosage unit form upon prescriptions shall be exempt from section 502(f)(1) of the act if all the following conditions are met:
(b) The label of the drug bears:
(3) If it is not subject to section 503(b)(1) of the act and is by custom among retail pharmacists sold in or from the interstate package for use by consumers, “adequate directions for use” in the conditions for which it is so sold.
Provided, however, That the information referred to in paragraph (b)(3) of this section may be contained in the labeling on or within the package from which it is to be dispensed.
[40 FR 13998, Mar. 27, 1975, as amended at 67 FR 4906, Feb. 1, 2002]