Lilly Warns of Impurities in Compounded Tirzepatide Drugs

Pharmaceutical company Eli Lilly has issued a warning regarding compounded versions of its blockbuster drugs Mounjaro and Zepbound, both containing the active ingredient tirzepatide. The concern centers around impurities found in compounded formulations that combine tirzepatide with vitamin B12.

What are Compounded Drugs?

Compounded drugs are not approved by the U.S. Food and Drug Administration (FDA) and may carry greater risks than FDA-approved treatments. They are created by combining, mixing, or altering ingredients to meet a patient’s specific needs, and are legally permitted when a patient requires a tailored medication due to medical concerns.

The Discovery of Impurities

Lilly’s laboratory testing revealed a chemical reaction between tirzepatide and vitamin B12, resulting in a molecule larger than tirzepatide alone. This interaction could potentially affect how the drug is absorbed, distributed, metabolized, or eliminated by the body. According to Lilly, “nothing is known” about the short- or long-term effects of this new molecule in humans, including its potential impact on efficacy, toxicity, or immune reactions [1].

The study, funded by Lilly, found significant levels of this impurity in all ten compounded samples tested. Inconsistent potency was similarly observed, with some samples containing as little as 43% of the labeled drug amount [4].

Why Add Vitamin B12?

Compounded versions of tirzepatide with added vitamin B12 gained popularity during shortages of the brand-name drugs. While the shortages have eased, some compounders continue to offer these mixtures, marketing them as personalized formulations. Vitamin B12 is involved in red blood cell formation and energy metabolism, and some compounders claim adding it to tirzepatide may support address fatigue, particularly in those with a deficiency [2]. However, there is no evidence to support the claim that adding B12 improves weight loss outcomes.

FDA Concerns and Approvals

The FDA warns that compounded products are not reviewed for safety, effectiveness, or quality [1]. Tirzepatide is approved under the brand names Mounjaro for type 2 diabetes and Zepbound for weight loss [2]. Zepbound is also approved for chronic weight management and obstructive sleep apnea (OSA).

Industry Response

Scott Brunner, CEO of the Alliance for Pharmacy Compounding (APC), stated that Lilly’s announcement raises “more questions than answers” and questioned the source of the samples used in Lilly’s testing. He noted that drugs from unlicensed websites or medical spas may not meet the same standards as those prepared by state-licensed compounding pharmacies [3].

What Should Patients Do?

Experts recommend that individuals currently using compounded GLP-1 medications discuss alternatives with their healthcare provider. If affordability or insurance coverage is a concern, exploring options for FDA-approved GLP-1s for conditions like obstructive sleep apnea or type 2 diabetes may be beneficial. The price gap between compounded and brand-name medications has also narrowed in some cases [2].

Key Takeaways

• Eli Lilly has identified an impurity in compounded tirzepatide drugs mixed with vitamin B12.
• The FDA does not approve compounded drugs, and they may pose risks to patient safety.
• Patients using compounded GLP-1 medications should consult with their healthcare provider.
• The impurity’s effects on humans are currently unknown.