Lilly finds impurity in compounded version of its weight-loss drug, warns of health risks

Compounded weight-loss drugs that contain vitamin B12 and the main ingredient in Eli Lilly's LLY.N Zepbound could present health risks to consumers due to a previously unidentified impurity caused in the preparation, the U.S. drugmaker said in a public letter released on Thursday.

The letter, based on Lilly's testing of samples of compounded products, is the company's latest move against drug compounders it says are marketing illegal copies of Zepbound and its diabetes drug Mounjaro. Both medicines have the same active ingredient, tirzepatide.

Lilly has sued compounders, wellness centers and other companies for selling products claiming to contain tirzepatide.

Compounders have argued their products are legal under a narrow provision of federal law that allows compounding when patients require personalization due to medical concerns, like the addition of vitamins or doses not available in the branded versions.

Lilly's testing of products obtained from compounding pharmacies, medspas and telehealth networks found "significant levels of an impurity that results from a chemical reaction between tirzepatide and B12," according to the letter and a scientific manuscript on the testing process shared with Reuters.

The impurity was identified in all ten samples tested by Lilly, the company said.

"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 posted on the company'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 notified the FDA of its findings and called for a nationwide recall of products containing both ingredients.

The FDA in September issued warning letters to 30 telehealth companies for making false or misleading claims about compounded versions of weight-loss drugs.

The agency also threatened action against "illegal copycat drugs" after telehealth company Hims & Hers Health HIMS.N said in February it would begin selling a compounded version of Novo Nordisk's NOVOb.CO Wegovy pill.

Hims quickly backed away from its compounded pill and announced plans this week to sell Novo's Wegovy and Ozempic on its platform.

-Leah Douglas/Reuters