Lilly is sounding the alarm on a growing safety risk for compounded tirzepatide mixed with vitamin B12. The pharmaceutical giant tested these products being marketed to Americans and found “significant levels of an impurity that results from a chemical reaction between tirzepatide and B12.”

 

“The impurity caused by the interaction between B12 and compounded tirzepatide is concerning because nothing is known about its short- or long-term effects in humans, the potential impact on the drug’s interaction with the GLP-1 and GIP receptors, toxicity, immune reactions, or how it is absorbed, distributed, metabolized and eliminated,” Lilly said.

 

The company warned that “the risks to patients are unknown because tirzepatide has never been studied in combination with B12 and the compounders making these combination drugs are not required to monitor or report adverse events.” 

 

Patients using tirzepatide-B12 products—whether from compounders, telehealth companies, medspas, or other sources—“may be using a potentially dangerous product with unknown risks,” Lilly said. The company has notified the FDA and recommends that patients “contact their physicians for advice and discussion on alternative treatment options.”

 

Lilly has long voiced concerns over mass-compounded knockoffs of its tirzepatide medicines, Mounjaro and Zepbound. 

 

The company “applaud[s] the FDA’s recent announcement of its intent to take decisive action against the mass distribution of illegally compounded anti-obesity drugs.” The FDA has repeatedly warned that compounded products “pose a higher risk” than FDA-approved medicines, noting that their safety, effectiveness, and quality are not reviewed.

 

Despite federal rulings confirming that mass-compounding of tirzepatide must stop, some companies continue to market “personalized” versions by adding untested ingredients like B12. 

 

Lilly said, “In reality, these products are not ‘personalized’ at all. Most sellers put the same untested additives in all their tirzepatide knockoffs to try to evade FDA regulations.” Testing shows these so-called “personalized” products “may pose even greater risks to patients than previously known.”

 

The discovery of the new B12-related impurity underscores the dangers of mixing untested additives with complex molecules like tirzepatide. “B12 is just one of the many untested additives used in the mass production of compounded GLP-1s under the guise of ‘personalization,’” Lilly said. 

 

Compounders are also combining tirzepatide with glycine, pyridoxine, niacinamide, carnitine, and other chemicals, creating “a range of new and untested combination drugs.” These additives “have no proven clinical benefit for patients taking tirzepatide, and the resulting combinations introduce unknown risks for patients.”

 

Lilly also continues to identify “other critical safety issues in compounded tirzepatide knockoffs, including bacterial contamination, high endotoxin levels, and other impurities that are not present in Lilly’s FDA-approved medicines.”

 

“The continued widespread distribution of untested compounded drugs is an unacceptable risk for patients,” Lilly said. 

 

The company urged regulators and law enforcement to take action and called on the FDA to “continue taking action against unlawful mass compounding of tirzepatide that puts the American public at risk, including by requesting a recall of all compounded tirzepatide combined with untested additives like B12.”