Eli Lilly and Co (NYSE:LLY) on Thursday issued a public warning about potential safety risks linked to compounded tirzepatide products that are mixed with vitamin B12.

The company said internal testing detected a previously unidentified impurity formed when the two substances interact.

The drugmaker evaluated compounded products marketed in the U.S. that combine tirzepatide with vitamin B12—also referred to as methylcobalamin, hydroxocobalamin, or cyanocobalamin.

Laboratory testing revealed significant levels of an impurity created through a chemical reaction between tirzepatide and the vitamin.

Unknown Health Effects Raise Safety Questions

Lilly said the newly identified impurity raises concerns because its effects in humans are unknown.

The company noted there is no data on how the compound could influence tirzepatide's interaction with GLP-1 and GIP receptors, or its potential toxicity, immune response, ...