Eli Lilly Warns of Safety Risks in Compounded Tirzepatide Mixed with Vitamin B12

Eli Lilly has issued a public warning regarding potential safety risks linked to compounded tirzepatide products mixed with vitamin B12.

As part of its ongoing commitment to patient safety, the biotech company conducted tests on compounded products marketed in the United States that combine tirzepatide with various forms of vitamin B12, including methylcobalamin, hydroxocobalamin, and cyanocobalamin. These tests identified significant levels of an impurity formed through a chemical reaction between tirzepatide and vitamin B12.

Unknown impurities and untested combinations raise serious concerns for patient safety, Eli Lilly says

This impurity raises serious concerns because its effects on humans remain entirely unknown. There is no available data on its short- or long-term impact, potential toxicity, or possible immunological reactions.

Additionally, it is unclear how this impurity interacts with GLP-1 and GIP receptors, or how it is absorbed, distributed, metabolized, and eliminated by the body. Tirzepatide has never been clinically studied in combination with vitamin B12, leaving a significant gap in safety knowledge. Compounding manufacturers are also not required to monitor or report adverse events, further increasing uncertainty around these products.

Eli Lilly cautions that individuals receiving tirzepatide-B12 combinations from compounding pharmacies, telemedicine providers, medspas, or other sources may be exposed to potentially dangerous products with unknown risks. The company has informed the U.S. Food and Drug Administration (FDA) of its findings and advises patients currently using such products to consult their healthcare providers to discuss safer, approved treatment alternatives.

The company has consistently voiced concerns about the safety of mass-produced tirzepatide imitations, including those marketed as alternatives to approved medications. Lilly supports the FDA’s recent announcement of plans to take stronger action against the widespread distribution of illegally compounded anti-obesity drugs. The FDA has repeatedly warned that compounded drugs carry greater risks than approved medications, as they are not subject to the same rigorous evaluation for safety, effectiveness, and quality.

Despite regulatory and legal efforts to halt the mass production of tirzepatide, some manufacturers continue to distribute these products under the label of “customized” treatments. In many cases, these so-called customized formulations simply involve adding untested substances, such as vitamin B12, to tirzepatide. According to Eli Lilly, these additions are not genuinely tailored to individual patients but are instead broadly applied in an attempt to bypass regulatory restrictions. Testing indicates that such combinations may introduce even greater risks than previously understood.

The issue extends beyond vitamin B12. Other additives, including glycine, pyridoxine, niacinamide, and carnitine, are also being mixed with tirzepatide without proper evaluation. These substances have no proven clinical benefit when combined with tirzepatide and may create new, untested drug combinations with unpredictable effects. Eli Lilly has also identified additional safety concerns in compounded tirzepatide products, such as bacterial contamination, elevated endotoxin levels, and other impurities not found in FDA-approved medications.

Eli Lilly emphasizes that the widespread distribution of these unassessed compounded drugs represents a significant and unacceptable risk to patients. The company urges regulators to continue enforcing existing laws and calls for the recall of compounded tirzepatide products containing untested additives like vitamin B12.

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