California Code, Health and Safety Code - HSC § 1385.0022

A pharmacy benefit manager has a fiduciary duty to its payer client that includes a duty to be fair and truthful toward the payer, to act in the payer's best interests, to avoid conflicts of interest, and to perform its duties with care, skill, prudence, and diligence.  This section does not limit a payer's obligations under applicable law with respect to the administration of health care coverage for plan participants.