Cal. Health & Saf. Code § 1320
A skilled nursing facility or intermediate care facility shall not require patients to purchase drugs, or rent or purchase medical supplies or equipment, from any particular pharmacy or other source.
This section shall not preclude a skilled nursing facility or intermediate care facility from requiring that the patient's pharmacy or other source comply with the facility's policies and procedures reasonably necessary for the care of the patient or policies and procedures required to meet the intent of state or federal regulations. Nothing in this section shall preclude a skilled nursing facility or intermediate care facility from requiring that controlled substances which are periodically counted by the facility on at least a daily basis be dispensed by the patient's pharmacy in containers suitable for that purpose.
Ca. Health and Saf. Code § 1320