Warning Issued Over Dangerous Counterfeit Weight-Loss Medications
Pharmacies and health providers are being urged to exercise extreme caution regarding counterfeit versions of popular weight-loss medications, Mounjaro and Zepbound. Eli Lilly, the pharmaceutical giant behind these blockbuster drugs, has issued an urgent warning due to the discovery of “critical safety issues” and “significant levels of an impurity” in compounded copies of tirzepatide, the active ingredient in both Mounjaro and Zepbound.
Compounded medications are often presented as customised alternatives to commercially available, FDA-approved drugs, designed to meet specific, unmet needs. While pharmacies are permitted to create compounded drugs, the U.S. Food and Drug Administration (FDA) does not subject these preparations to the same rigorous safety and quality reviews as approved medications. This lack of oversight significantly increases the risk of improper dosages and contamination.
The Dangers of Compounded Tirzepatide-B12 Combinations
Eli Lilly’s investigation revealed impurities in compounded drugs that combine tirzepatide with vitamin B12. The company stated these impurities arose from a “chemical reaction” between tirzepatide and B12. More alarmingly, Lilly highlighted that the risks to patients are entirely unknown, as tirzepatide has never been studied in combination with B12. Furthermore, the compounders producing these combined drugs are not mandated to monitor or report adverse events.
“People receiving tirzepatide-B12 products from compounders, telehealth companies, medspas or anyone else should be aware that they may be using a potentially dangerous product with unknown risks,” a statement from Lilly cautioned.
This warning follows a recent announcement from the FDA, indicating that the agency would be implementing “decisive steps” to curb the sale of non-FDA-approved compounded weight-loss drugs. The aim is to “safeguard consumers from drugs for which the FDA cannot verify quality, safety or efficacy.”
Eli Lilly noted that despite federal confirmations that the mass compounding of tirzepatide must cease, some entities persist, claiming to offer “personalised” versions by adding untested additives, such as B12, to compounded tirzepatide. Lilly asserts these products are not personalised at all, with most sellers adding the same untested substances to evade FDA regulations. The company’s testing of these so-called “personalised” compounded tirzepatide products suggests they may pose even greater risks to patients than previously understood.
The Rise of Compounded GLP-1s and Patient Demand
The popularity of GLP-1 medications, including Mounjaro, Zepbound, and Ozempic, has surged. Data from November 2025 by the Kaiser Family Foundation indicated that one in eight Americans has tried a GLP-1 for weight loss, diabetes, or conditions like Polycystic Ovary Syndrome (PCOS). This figure has doubled since a February 2024 Gallup poll, which showed approximately six percent of Americans had used these drugs.
Compounded GLP-1 drugs gained traction in recent years amidst shortages of key medications like tirzepatide and semaglutide (the active ingredient in Ozempic and Wegovy). They also often present a more affordable alternative, with prices ranging from $130 to $450 per month compared to over $1,000 for conventional versions without insurance.
Legal Action and Further Concerns
In addition to FDA warnings, Eli Lilly and Novo Nordisk, the maker of Ozempic, have initiated legal proceedings against compound distributors, including Hims. Earlier this month, Hims announced it would cease marketing these drugs as part of a settlement with Novo Nordisk.
While the exact nature of the impurity resulting from the tirzepatide and vitamin B12 combination remains unclear, Lilly believes its findings underscore the dangers of haphazardly mixing untested additives with complex molecules like tirzepatide without rigorous testing, clinical trials, and FDA approval.
While vitamin B12 is generally considered safe, elevated doses can be detrimental for individuals with chronic kidney or liver disease, as their bodies struggle to eliminate it effectively. Furthermore, according to the Mayo Clinic, there is no substantial evidence to suggest that B12 aids in weight loss.
“B12 is just one of the many untested additives used in the mass production of compounded GLP-1s under the guise of ‘personalisation’,” Eli Lilly stated.
Beyond B12: A Spectrum of Unsafe Additives
Eli Lilly has also reported that several companies selling compounded GLP-1s have incorporated other substances into tirzepatide, including vitamins B3 and B6, and the amino acid compound carnitine. The safety and efficacy of these combinations remain unknown.
“These additives have no proven clinical benefit for patients taking tirzepatide, and the resulting combinations introduce unknown risks for patients,” Lilly elaborated. “We also continue 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.”
The FDA has previously documented reports of compounded GLP-1s being improperly stored without refrigeration or manufactured with substandard ingredients. Adverse reactions observed in such cases include redness, swelling at the injection site, pain, and the development of a red lump.
Eli Lilly concluded with a strong call to action: “The continued widespread distribution of untested compounded drugs is an unacceptable risk for patients. We also urge 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.”
