Lilly calls for recall after finding impurity in compounded tirzepatide with vitamin B12

Eli Lilly said on March 12, 2026, that its testing of tirzepatide sold by compounding pharmacies turned up a previously unidentified impurity created when the drug is mixed with vitamin B12, and the company asked for a nationwide recall of products containing both ingredients ^[1][2].

Lilly laid out the findings in an open letter and in a scientific manuscript titled "A Novel, Widespread Impurity in Mass-Compounded Tirzepatide/B12 Products" ^[1][3]. The impurity appeared in all 10 samples the company tested, according to Reuters ^[2].

The samples came from compounding pharmacies, medspas and telehealth networks, the letter and the manuscript shared with Reuters say ^[2]. Product labels may list the B12 as methylcobalamin, hydroxocobalamin or cyanocobalamin ^[1].

Lilly said it does not know what the impurity does in the body. Its short- and long-term effects in humans have not been studied, nor have its toxicity, whether it provokes immune reactions, how it is absorbed and cleared, or whether it changes how tirzepatide acts on the GLP-1 and GIP receptors ^[1]. Tirzepatide has never been tested alongside B12 in the same solution, the company said, and the businesses making the combination are not required to track or report side effects ^[1].

"FDA warns that compounded products can be risky for patients because they are not reviewed for safety, effectiveness, or quality," Lilly chief medical officer David Hyman said in a statement. "Adding a reactive substance like vitamin B12 without clinical testing or FDA review introduces additional unknown risks." ^[2]

Lilly said it told the FDA about its results and wants a nationwide recall of products holding both ingredients, and it urged other regulators and law enforcement to act as well ^[1][2]. The company also told people using tirzepatide-B12 products to contact their doctors about other treatment options ^[1].

Compounders disputed the characterization. Scott Brunner, chief executive of the Alliance for Pharmacy Compounding, called the findings concerning but said Lilly would need to describe how it collected and tested the samples before anyone could judge the real danger. "Based on what I've read so far, Lilly isn't telling us enough to make that determination," he said ^[2].

Compounding pharmacies have argued that their versions are legal under a narrow part of federal law that permits customizing a medicine for a patient's medical needs, such as adding a vitamin or supplying a dose the brand does not sell ^[2]. Lilly rejects that description, saying most sellers put the same additives into every batch rather than tailoring anything to an individual ^[1].

B12 is not the only additive Lilly named. The letter also lists glycine, pyridoxine, niacinamide and carnitine, saying the company has found no proven clinical benefit for tirzepatide patients from those combinations. Lilly said its testing has also turned up bacterial contamination, high endotoxin levels and other impurities that it does not find in its own FDA-approved medicines ^[1].

Why it matters for patients

Tirzepatide reaches patients two ways: as Mounjaro or Zepbound, which the FDA approved, and as a compounded drug from a compounding pharmacy, telehealth company or medspa ^[1][2]. Someone buying a compounded vial may not be told whether B12 is in it, because Lilly says sellers tend to use the same additive mix across their products ^[1].

What the impurity would mean for a person's health is unresolved. Nothing in the published material identifies its chemical structure, states whether harm occurs at the levels Lilly measured, or estimates how many people use these combinations. Lilly said that because compounders are not required to report adverse events, problems tied to these products may go unrecorded ^[1]. Brunner's request for sampling details means the disagreement over the testing itself is still open ^[2].

What happens next

Lilly's recall request now sits with the FDA, and no decision has been reported ^[1].

The FDA has sent warning letters to 30 telehealth companies over false or misleading claims about compounded weight-loss drugs ^[2]. The agency also threatened action against "illegal copycat drugs" after Hims & Hers Health said in February it would begin selling its own version of Novo Nordisk's Wegovy pill; the company backed away from that plan and announced it would instead sell Novo's Wegovy and Ozempic on its platform ^[2].