A veterinarian must document the prescribing of all prescription medications, including controlled substances, in the patient’s medical record. See N.Y. Guideline 5: Professional Practice § 5.14. 

The information should include the name and strength of the drug prescribed, the amount prescribed, and the directions given to the client for administration of the medication. Practitioners may choose to place a copy of an official prescription in the patient record, but it is not required.