By Sriparna Roy and Christy Santhosh

(Reuters) -Eli Lilly has sent cease-and-desist letters to U.S. healthcare providers in recent days to stop the promotion of the compounded versions of its drugs for weight loss and diabetes, as their supply increases, the company said on Wednesday.

The letters were sent to telehealth companies, wellness centers and medical spas selling compounded versions of the drugmaker’s popular treatments Zepbound and Mounjaro, a spokesperson told Reuters.

“When FDA-approved medicines are ‘commercially available’, compounders cannot regularly make ‘essentially a copy’ of them,” the company said in its emailed statement.

Compounded drugs are custom-made medicines that are based on the same ingredients as branded drugs. Because Zepbound and Mounjaro, both known chemically as tirzepatide, were in short supply, they could be legally produced by licensed pharmacies in the U.S.

Surging demand for Lilly and Danish rival Novo Nordisk’s weight-loss drugs, which have been shown to help patients lose as much as 20% of their weight, has prompted numerous sellers to offer compounded versions that may cost more than $1,000 for a month’s supply.

Lilly and Novo have previously sued more than three dozen medical spas, weight-loss clinics, compounding pharmacies and online sellers in total to stop them from selling products claiming to contain the active ingredients in their drugs.

The U.S. Food and Drug Administration has listed all doses of Lilly’s drugs as available but has not removed them from the shortage list.

One dose of Novo’s weight-loss drug, Wegovy, is currently on the FDA’s shortage list.

The FDA said in an emailed response that it was currently working to determine if the available supply of tirzepatide, the active ingredient in Mounjaro and Zepbound, would meet its definition of a resolved shortage.

Bloomberg, which was the first to report the news, said several brick-and-mortar clinics also received letters from Lilly, demanding that they stop the “manufacture, promotion, and/or sale” of compounded versions of Mounjaro and Zepbound.

(Reporting by Sriparna Roy and Christy Santhosh in Bengaluru; Editing by Vijay Kishore, Patrick Wingrove and Anil D’Siva)