Isonicotinic acid hydrazide’s common name — a powerful antibiotic treating tuberculosis in humans and animals. Some countries strictly ban treating dairy cattle with isoniazid, since it can disrupt the tuberculin test, and residues in milk remain a potential hazard to human health. It illustrates how veterinary drug controls protect both disease-surveillance programmes and the wider milk supply — two public-health goals that a single residue violation could undermine. Milk testing programmes routinely screen for such drug residues to protect consumers.