Testing reveals that compounded tirzepatide products mixed with vitamin B12 contain a chemical impurity of unknown toxicity.
Eli Lilly issued a public safety warning regarding compounded versions of tirzepatide mixed with vitamin B12.
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In an open letter released from the company, Eli Lilly says testing has revealed a potentially dangerous chemical impurity in products being marketed to Americans outside of the FDA-approved supply chain.
"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," said David Hyman, Lilly's chief medical officer.
According to a statement from the company’s website, Lilly tested compounded products containing tirzepatide combined with B12, marketed under the names methylcobalamin, hydroxocobalamin, or cyanocobalamin, and found significant levels of an impurity produced by a chemical reaction between the two substances.1
The company says nothing is known about the impurity's short- or long-term effects in humans, its impact on how tirzepatide interacts with GLP-1 and GIP receptors, its toxicity, or how it is processed by the body.1 Because compounders are not required to monitor or report adverse events, there is no safety data available on the combination.
Lilly has notified the FDA of its findings and is recommending that anyone using tirzepatide-B12 products, either obtained through compounders, telehealth companies, medspas, or other sources, contact their physician to discuss alternative treatment options.1
Lilly has notified FDA of its discovery and has requested a nationwide recall of products containing both ingredients.2
Lilly says B12 is just one of many untested additives being mixed with compounded tirzepatide by manufacturers claiming to offer personalized versions of the drug. Others include glycine, pyridoxine, niacinamide, and carnitine.1
The company says these additives have no proven clinical benefit for patients taking tirzepatide and that the resulting combinations introduce unknown risks. Lilly also says its ongoing testing of compounded tirzepatide products continues to find bacterial contamination, high endotoxin levels, and other impurities not present in its FDA-approved medicines, Mounjaro and Zepbound.1
Eli Lilly characterized the personalization framing used by compounders as a tactic to evade FDA regulations following court rulings and
"Most sellers put the same untested additives in all their tirzepatide knockoffs," Lilly said, arguing the products are not personalized in any meaningful sense.
Lilly urged the FDA to continue to take action against unlawful mass compounding of tirzepatide and specifically called on the agency to request a recall of all compounded tirzepatide products combined with untested additives including B12.1
The company also called on other regulators and law enforcement to act, describing the continued widespread distribution of untested compounded drugs as an unacceptable risk to patients.
Eli Lilly’s warning comes as the FDA has already signaled its intent to take decisive action against the mass distribution of illegally compounded anti-obesity drugs, a move Lilly publicly praised while pressing for further enforcement.
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