The news: Eli Lilly issued a warning about the safety risks tied to compounded tirzepatide and vitamin B12. Its testing detected “significant levels” of a reaction-related impurity in all 10 samples Lilly obtained from compounding pharmacies, telehealth companies, and med spas.

Lilly also notified the US Food and Drug Administration (FDA) about its findings and is calling for a nationwide recall of those compounded products.

Catch up quick: Tirzepatide is the active ingredient in Lilly’s GLP-1 drugs Mounjaro and Zepbound. B12 is a common additive used to make “personalized” compounded weight-loss drugs. The FDA allowed widespread compounding during GLP-1 drug shortages from 2022 to 2025, but now some companies continue to do so under rules allowing customized doses.

Why it matters: Lilly’s warning is the latest move by GLP-1 drugmakers, including chief competitor Novo Nordisk, to rein in compounders alongside increased FDA scrutiny.

• Lilly and Novo have both filed multiple lawsuits against compounders over the past several years, alleging unsafe or unlawful marketing and manufacturing practices.
• Earlier this month, the FDA sent 30 warning letters to telehealth companies over false or misleading claims tied to compounded GLP-1 weight-loss drugs. That followed 50 similar letters sent in September.

That pressure is already reshaping telehealth strategy. Novo recently dropped its lawsuit against Hims & Hers after they reached a deal for Hims to sell branded Wegovy (semaglutide) on its website. Hims agreed to stop advertising compounded GLP-1s but said it will continue selling personalized versions to some patients when a doctor deems them clinically appropriate.

Implications for weight loss drugmakers and telehealth: Lilly’s warning introduces specific formulation concerns into an already intensifying legal and regulatory fight over compounded GLP-1s. By pointing to reaction-related impurities, it's giving regulators and consumers a concrete safety issue to consider.

For telehealth platforms and compounders, it increases scrutiny over how personalized versions are formulated and mixed—not just how they are marketed. Companies may face a choice to either defend the clinical rationale for customized combinations or shift to partnerships with FDA-approved branded drugs.

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