LONDON, Nov 1 (Reuters) - Novo Nordisk is spending billions of dollars to boost output and ease shortages of its hugely popular, highly effective weight-loss medicine Wegovy.

The Danish drugmaker, which reports its third-quarter results on Nov. 2, has warned U.S. demand will continue to outpace supplies of the weekly self-injection into 2024.

Novo depends upon a number of companies to help produce Wegovy, but it has released scant details on its supply chain for the weight-loss medicine and its diabetes drug Ozempic containing the same active ingredient.

Here are the details of the manufacturing supply chain, based on public statements by Novo and Reuters' reporting:

ACTIVE PHARMACEUTICAL INGREDIENT (API)

The active pharmaceutical ingredient (API) contained in Wegovy is called semaglutide. Novo says that it produces all of the API for Wegovy at its facilities in Denmark.

FILL-FINISH

Novo has hired Catalent, a large U.S. contract drug manufacturer, to fill injection pens for Wegovy at two of that company's plants: in Brussels and in Bloomington, Indiana.

Novo has also hired another U.S. firm, Thermo Fisher , as a Wegovy pen filler. That company is performing the work at its factory in Greenville, North Carolina.

It has said it will sign up a third by the end of the year but has not identified the company. Thermo is converting a building that makes tablets and pills at the Greenville site to do sterile fill-finish work instead, a company spokesperson told Reuters last week.

ASSEMBLY AND PACKAGING

At its most recent capital markets day, in March 2022, Novo said it assembled and packaged Wegovy at its own facilities.

In September, Reuters reported that Novo had hired U.S. private company PCI Pharma Services to handle some assembly and packaging of the drug.

Assembling the pens after a glass cartridge is filled with Wegovy is the final stage of manufacturing before it is shipped.

COMPONENTS

The Wegovy injection pens for the U.S. market slightly differ from those sold in the European markets including Norway, Denmark, Germany and UK, where it has so far launched.

The pen for Europe uses the so-called FlexTouch device and contains four doses per pen, instead of one in the U.S. pen.

Both pen devices contain a number of components. They include, depending on the device: a glass cartridge or a glass syringe, a pre-filled plastic pen, a needle shield, and a rubber plunger.

Swiss medical technology company Ypsomed in September announced a long-term supply deal with Novo for autoinjectors, another component contained in the pens.

Several large companies have said they are making these components for companies manufacturing injection drugs from the GLP-1 receptor class to which Wegovy belongs.

These companies include West Pharmaceutical Services , Stevenato Group SpA, Gerresheimer and SCHOTT Pharma. (Reporting by Maggie Fick Editing by Josephine Mason and Tomasz Janowski)