Novo Nordisk on Monday said it is ending its collaboration with Hims & Hers due to concerns about the telehealth company’s sales and promotion of cheaper knock-offs of the weight loss drug Wegovy. 

Shares of Hims & Hers fell about 20% in premarket trading Monday. 

Novo Nordisk in April said it would offer Wegovy through several telehealth companies such as Hims & Hers to expand access to the blockbuster injection now that it is no longer in short supply in the U.S. 

The end of the Wegovy shortage meant compounding pharmacies were legally restricted from making and selling cheaper, unapproved versions of Wegovy – with rare exceptions. Telehealth companies have said patients may still need personalized compounded versions of Wegovy due to medically necessary reasons, such as having allergies to certain ingredients in the branded product. 

But Novo Nordisk on Monday said Hims & Hers has “failed to adhere to the law which prohibits mass sales of compounded drugs” under the “false guise” of personalization. The drugmaker also accused Hims & Hers of “deceptive” marketing that is putting patient safety at risk.

A Hims & Hers spokesperson did not immediately respond to CNBC’s request to comment.