Eli Lilly has issued an open letter warning of a potentially dangerous chemical impurity found in compounded versions of Tirzepatide that have been mixed with Vitamin B12.
Discovery of unknown chemical impurities
Testing conducted by Eli Lilly on products marketed outside the FDA-approved supply chain revealed a significant chemical reaction. When Tirzepatide is compounded with Vitamin B12 variants (such as methylcobalamin or cyanocobalamin), it produces an impurity of unknown toxicity.
The company stated that nothing is known about the short- or long-term clinical effects of this impurity, its impact on receptor interactions, or how it is processed by the human body. Unlike official manufacturers, compounders are not required to monitor or report adverse events, leaving a critical gap in safety data for these combinations.
[Image illustrating the chemical incompatibility between Tirzepatide and B12 additives]
Pushing for regulatory enforcement
Beyond B12, Eli Lilly identified several other unproven additives—such as glycine, niacinamide, and carnitine—being used by manufacturers claiming to offer “personalized” medicine. Lilly characterized this framing as a tactic to evade FDA regulations following mandates to stop mass compounding of Tirzepatide now that official supply has stabilized.
Citing ongoing findings of bacterial contamination and high endotoxin levels in compounded samples, Eli Lilly has urged the FDA and law enforcement to take the following steps:
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National Recall: Request a nationwide recall of all compounded products containing Tirzepatide mixed with untested additives.
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Stricter Oversight: Halt the unlawful mass distribution of “knockoff” drugs through telehealth platforms, medspas, and other non-traditional sources.