Cal. Lab. Code § 4600.1

(a) Subject to subdivision (b), any person or entity that dispenses medicines and medical supplies, as required by Section 4600, shall dispense the generic drug equivalent.
(b) A person or entity is not required to dispense a generic drug equivalent under either of the following circumstances:
1. (1) When a generic drug equivalent is unavailable.
2. (2) When the prescribing physician specifically provides in writing that a nongeneric drug must be dispensed.
(c) For purposes of this section, “dispense” has the same meaning as the definition contained in Section 4024 of the Business and Professions Code.
(d) Nothing in this section shall be construed to preclude a prescribing physician, who is also the dispensing physician, from dispensing a generic drug equivalent.
(e) This section shall only apply to medicines dispensed prior to the operative date of the drug formulary adopted pursuant to Section 5307.27.