New Delhi: American drugmaker Eli Lilly and Company, makers of popular anti-obesity and diabetes drugs Mounjaro and Zepbound, Thursday warned about potential safety risks linked to compounded versions of tirzepatide that is being mixed with vitamin B12 and sold in the United States—a development medical experts say has little relevance for India at present.
Compounded tirzepatide is a custom-made version of the active ingredient of the weight-loss drug tirzepatide. It includes ingredients like glycine or B12.
Tirzepatide is the active ingredient in Lilly’s medicines Mounjaro (for Type 2 diabetes) and Zepbound (for chronic weight management). The company launched Mounjaro in India in March 2025.
In an open letter released on Thursday, the company said laboratory testing of compounded tirzepatide products being marketed in the US had detected “significant levels of an impurity” created when the drug reacts chemically with vitamin B12. “The impurity caused by the interaction between B12 and compounded tirzepatide is concerning because nothing is known about its short- or long-term effects in humans,” the company said.
Mounjaro and Zepbound are a new generation of metabolic drugs broadly grouped with GLP-1–based medicines that have reshaped diabetes and obesity treatment over the past few years. These medicines mimic hormones involved in appetite regulation, insulin secretion and glucose control.
Tirzepatide is distinct because it acts on two hormone pathways—GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) receptors—helping improve blood sugar control while also reducing appetite. Demand for these medicines has surged globally, particularly for obesity treatment.
“Compounded drugs are not approved by the U.S. Food and Drug Administration and are often allowed during drug shortages,” Dr Ambrish Mithal, chairman and head of Endocrinology and Diabetes at Max Healthcare, told ThePrint.
In the United States, high demand, supply constraints and high prices have contributed to the growth of a parallel market of “compounded” versions. Because tirzepatide remains under patent, such products are typically made by sourcing raw material and modifying the formulation with additional substances.
“In reality, these products are not ‘personalised’ at all,” the company said, referring to sellers who add substances such as vitamin B12, and market the resulting formulations as customised therapies.
Lilly said it has informed the US Food and Drug Administration about the findings, and urged patients using such products to consult physicians about alternative treatment options.
‘US-specific issue’
Indian medical experts say the issue largely reflects the regulatory and market conditions in the United States. Dr Mithal said that compounded tirzepatide-like formulations are typically prepared by pharmacies rather than pharmaceutical companies.
Chennai-based diabetologist Dr V. Mohan, an obesity researcher and chairman of the Madras Diabetes Research Foundation (MDRF), said such formulations are not being manufactured or marketed in India currently. Dr Mohan said that the issue has arisen in the US. “What they’re doing is importing some raw material equivalent of tirzepatide and then adding something like B12 to say this is not tirzepatide but something else,” he said.
While medicines in the broader GLP-1 class like semaglutide are beginning to see generic or off-patent versions in several countries, including India, tirzepatide itself remains under patent protection globally.
(Edited by Nardeep Singh Dahiya)
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