21 CFR § 1306.23 - Partial filling of prescriptions.
The partial filling of a prescription for a controlled substance listed in Schedule III, IV, or V is permissible, provided that:
(a) Each partial filling is recorded in the same manner as a refilling,
(b) The total quantity dispensed in all partial fillings does not exceed the total quantity prescribed, and
(c) No dispensing occurs after 6 months after the date on which the prescription was issued.