Food and Drug Administration requires require a Veterinary Feed Directive (VFD) or a prescription for all medical antibiotics to be used in feed for food animal species. A VFD can only be issued from a licensed veterinarian, based on a valid veterinarian-client-patient relationship before a producer may use feeds containing antibiotics that are medically important (including complete feeds, medicated supplements and crumbles) to human health. A veterinarian can write a VFD that is effective for up to six months.