The mechanism. Compounding pharmacies aren't allowed to mass-produce copies of patented drugs — except when the FDA's drug shortage list says a branded product is unavailable. That exception is what let thousands of med spas and telehealth startups sell cheap tirzepatide and semaglutide knockoffs for two years while Eli Lilly and Novo Nordisk couldn't make enough Zepbound and Wegovy to meet demand. The moment FDA declares the shortage "resolved," the legal basis for that copycat supply chain evaporates — 503A pharmacies and 503B outsourcing facilities get a wind-down window (60-90 days historically) and then must stop. No congressional vote, no new statute — just an administrative determination in the Federal Register. FDA already pulled tirzepatide (December 2024) and semaglutide (February 2025) off the shortage list this way, and on April 30, 2026 it went further, proposing to strip semaglutide, tirzepatide, and liraglutide off the 503B "clinical need" bulks list entirely — a move that would foreclose bulk compounding even during future shortages. Public comment closed June 29, 2026; a final rule is the next catalyst.