California Code, Business and Professions Code - BPC § 19581

No substance of any kind shall be administered by any means to a horse after it has been entered to race in a horse race, unless the board has, by regulation, specifically authorized the use of the substance and the quantity and composition thereof. The board may require that the official veterinarian approve, in writing, the administration of those substances in accordance with the regulations of the board. Any medication or equipment used to dispense medication that is located within the inclosure is subject to search and inspection at the request of any board official.