HQ Staff Writer
March 13, 2026: Eli Lily, the pharmaceutical giant, has warned that compounded versions of its blockbuster weight-loss drug tirzepatide, when mixed with vitamin B12, contain a previously unknown chemical impurity that poses potentially serious health risks, prompting the company to notify the U.S. Food and Drug Administration and call for an immediate recall of all such products.
The warning is about compounded tirzepatide, the active ingredient in Lilly’s FDA-approved drugs Mounjaro and Zepbound being sold by compounding pharmacies, medspas, and telehealth companies combined with vitamin B12, also known as methylcobalamin, hydroxocobalamin, or cyanocobalamin. Lilly 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. The impurity was identified in all ten samples tested by Lilly.
The impurity 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, metabolised and eliminated.
‘Personalised’ in name only
The warning arrives at a charged moment in the battle between Eli Lilly and the sprawling grey market of compounded GLP-1 drugs. After surging demand for Mounjaro and Zepbound created widespread shortages, hundreds of compounders began manufacturing their own tirzepatide products — often at a fraction of the brand-name cost. Branded versions of tirzepatide can run over $1,000 a month without insurance, while compounded alternatives were frequently available for $150 to $600.
When the FDA removed tirzepatide from its drug shortage list in late 2024, it ordered compounders to stop. Many pivoted to a legal loophole: adding vitamins like B12 to their formulations, arguing this made their products sufficiently ‘personalised’ to remain lawful. In reality, these products are not personalised at all. Most sellers put the same untested additives in all their tirzepatide knockoffs to try to evade FDA regulations.
Lilly’s Chief Legal Officer David Hyman addressed the safety angle directly. “FDA 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,” he said.
Wider contamination problem
B12 is not the only cause for concern. Mass compounders and supposed ‘personalizers’ are also mixing tirzepatide with glycine, pyridoxine, niacinamide, carnitine, or 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.
Lilly also continues to find 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. In earlier investigations, the company found at least one compounded product that turned out to be nothing more than sugar alcohol.
Lilly has formally notified the FDA of its findings and is urging the agency to request a recall of all compounded tirzepatide products combined with B12 or other untested additives. People receiving tirzepatide-B12 products from compounders, telehealth companies, medspas, or anyone else should contact their physicians for advice and discussion on alternative treatment options.
The company also praised the FDA’s recent announcement of decisive action against the mass distribution of illegally compounded anti-obesity drugs, and called on other regulators and law enforcement to follow suit.
For patients locked out of brand-name drugs by cost, Lilly has introduced lower-priced single-dose vials of Zepbound at approximately $399 per month, and offers savings cards for commercially insured patients though the price gap with compounded alternatives remains significant for many.
