"Novo Nordisk has seen a significant increase in illegal online sales," the company said in a statement, referring to products that contain the active ingredient semaglutide.

Amid a global obesity crisis, Novo became Europe’s most valuable company this year on soaring demand for weekly injection Wegovy and its lower-dose version Ozempic, but this has attracted illegal traders who may put users' health at risk.

Novo's words of caution amounted to the first detailed comments from the group on the counterfeit issue since a mid-June statement about fake Ozempic pens found at a US retail pharmacy.

The warning came after Germany's federal drug regulator on Wednesday urged pharmacies and drug distributors to be vigilant following the discovery of wholesale batches of fake Ozempic.