What must a veterinarian obtain before prescribing an extra-label drug?

A veterinarian must obtain informed consent from the client before prescribing an extra-label drug because this process ensures that the client is fully aware of the risks, benefits, and potential alternatives associated with using a medication that is not specifically approved for the intended use in that animal. Extra-label use involves certain risks, and the veterinarian has an ethical and legal responsibility to communicate these to the client, allowing them to make an informed decision about their pet's treatment. This consent is crucial not only for building a trusted veterinarian-client relationship but also as a safeguard to ensure that clients understand the implications of the extra-label use of drugs for their animals.