Eli Lilly has publicly warned that compounded formulations of tirzepatide (the active ingredient in Zepbound/Mounjaro) that include vitamin B12 or other additives can generate a previously undetected impurity with unknown safety implications. Lilly has asked regulators to recall personalized compounded tirzepatide products and urged swift enforcement against compounding practices it calls risky. The company cited laboratory testing that identified chemical reactions between tirzepatide and B12 leading to a concerning impurity; Lilly said the findings raise short‑ and long‑term safety unknowns. The announcement amplifies regulatory scrutiny of telehealth firms and compounding pharmacies that have marketed “personalized” GLP‑1 formulations during high demand for obesity medicines. Regulators and industry observers say the dispute underscores manufacturing and supply‑chain pressure points for metabolic drugs: branded manufacturers are expanding manufacturing, while compounding and telemedicine channels create enforcement and pharmacovigilance complexities. The company’s request to FDA for recalls could prompt rapid regulatory guidance and legal actions that affect distribution channels and patient access.