Eli Lilly warned that compounded versions of its tirzepatide weight‑loss drug mixed with vitamin B12 can produce an unknown impurity that may affect the drug’s safety profile, efficacy, and pharmacokinetics. The company’s statement, issued on March 12, identified the impurity as a result of a chemical reaction between tirzepatide and B12 and noted that its health risks are currently unknown.
The warning followed testing of samples from compounding pharmacies, telehealth providers, and medspas. Lilly’s action reflects a broader effort to counter unregulated compounded tirzepatide products that have been marketed as “personalized” alternatives to its FDA‑approved drugs, Mounjaro and Zepbound.
By publicly flagging the risk, Lilly aims to protect its market share for its approved tirzepatide products. The alert could prompt regulatory scrutiny of compounding pharmacies and reduce patient demand for these unapproved alternatives, thereby strengthening Lilly’s competitive position in the weight‑loss market.
Lilly’s chief medical officer David Hyman said, “FDA warns that compounded products can be risky for patients because they are not reviewed for safety, effectiveness or quality. Adding a reactive substance like vitamin B12 without clinical testing or FDA review introduces additional unknown risks.” The company also warned that the impurity could alter the drug’s safety profile, efficacy, and pharmacokinetics.
The Alliance for Pharmacy Compounding CEO Scott Brunner criticized the warning for lacking specifics, noting that B12 is a well‑studied drug and that there has been no alarming trend of adverse events associated with compounded tirzepatide‑B12 over the past four years. He said Lilly had not provided enough information about the source of the samples or the magnitude of the impurity for anyone outside the company to evaluate the claim.
The safety alert underscores the tension between pharmaceutical manufacturers and compounding pharmacies and signals that Lilly is willing to use regulatory channels to defend its intellectual property and market position, potentially strengthening its competitive stance in the weight‑loss drug market.
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