March 7 (Reuters) - Eli Lilly ( LLY ) said on Thursday

it has found bacteria and high levels of impurities in products

claiming to be compounded versions of tirzepatide, the active

ingredient in its popular diabetes drug Mounjaro and weight loss

treatment Zepbound.

The U.S. drugmaker has sued several medical spas,

weight-loss clinics and compounding pharmacies to stop them from

selling products purporting to contain tirzepatide.

Compounded drugs are custom-made medicines based on the same

ingredients as branded versions, and often cheaper, but also

subject to less regulatory scrutiny.

In an open letter, Lilly said some of these products had a

different chemical structure as well as a different color than

the approved versions of Mounjaro or Zepbound.

"In at least one instance, the product was nothing more than

sugar alcohol," Lilly said.

The Alliance for Pharmacy Compounding, which represents

compounding pharmacists and technicians, did not immediately

respond to a request for comment.

The United States allows licensed pharmacies to legally

produce compounded drugs when the branded version of a drug is

in short supply.

Lilly, however, said it does not sell or provide tirzepatide

to any compounding pharmacies.

Danish rival Novo Nordisk has also taken legal

action against those offering products that claim to contain

semaglutide, the active ingredient in its popular weight loss

drug, Wegovy.

Novo reported in December it had found some samples of

compounded semaglutide to be up to 33% impure.

(Reporting by Bhanvi Satija in Bengaluru; Editing by Shinjini

Ganguli)