Eli Lilly (NYSE:LLY) said compounded weight-loss treatments that combine vitamin B12 with the active ingredient used in its Zepbound drug may pose health risks because of a newly identified impurity formed during preparation, according to a public letter released by the U.S. pharmaceutical company on Thursday.
The letter, based on Lilly’s testing of compounded products, marks the company’s latest effort to challenge drug compounders that it says are producing and marketing unauthorized copies of Zepbound and its diabetes therapy Mounjaro. Both medicines contain the same active ingredient, tirzepatide.
Lilly has filed lawsuits against compounding pharmacies, wellness clinics and other businesses accused of selling products advertised as containing tirzepatide.
Compounders, however, have argued that their formulations are permitted under a specific federal law provision that allows customized drug compounding when patients require personalized treatment, such as adding vitamins or providing doses not available in the branded medicines.
Testing conducted by Lilly on samples obtained from compounding pharmacies, medspas and telehealth providers found “significant levels of an impurity that results from a chemical reaction between tirzepatide and B12,” according to the letter and a scientific paper describing the testing process that was shared with Reuters.
The company said the impurity appeared in all ten samples analyzed during the testing.
“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,” said the letter, which was published on Lilly’s website.
“FDA (the U.S. Food and Drug Administration) 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.
Lilly said it had informed the FDA about the findings and urged regulators to issue a nationwide recall for products that contain both tirzepatide and vitamin B12.
In September, the FDA sent warning letters to 30 telehealth companies over what it described as false or misleading claims about compounded weight-loss medications.
The agency has also warned it could take action against what it called “illegal copycat drugs” after telehealth firm Hims & Hers Health (NYSE:HIMS) said in February that it planned to sell a compounded version of Novo Nordisk’s Wegovy pill.
Hims later reversed course on the compounded product and announced this week that it plans to offer Novo’s Wegovy and Ozempic through its platform instead.