The World Health Organisation and US drug manufacturer Eli Lilly have warned people to be wary of fake versions of popular weight loss and diabetes medicines.

The WHO said on Thursday that it has received reports of fake semaglutide — the active ingredient in Novo Nordisk’s Wegovy and Ozempic — in all regions of the world since 2022.

Lilly said in an open letter that it was “deeply concerned” about growing online sales and social media posts involving phony or compounded versions of tirzepatide, the active ingredient behind its drugs Mounjaro and Zepbound.

The Indianapolis-based company said it was the only lawful supplier of those drugs, and it does not provide tirzepatide to compounding pharmacies, wellness centres or online retailers.

Lilly said fake versions of its drugs frequently advertised or sold online are never safe to use.

Novo Nordisk has issued similar warnings in the past about its medicinces.

The WHO said patients can protect themselves by using prescriptions from licensed doctors. The agency said patients should avoid buying the drugs from unfamiliar sources.

Lilly said any products marketed as tirzepatide and not Mounjaro or Zepbound were not made by the drug maker and are not approved by the US Food and Drug Administration.