By Isabelle Yr Carlsson and Maggie Fick

COPENHAGEN/LONDON June 24 (Reuters) - Obesity drug-maker

Novo Nordisk will spend $4.1 billion to build a U.S.

facility to fill injection pens for its hugely popular

weight-loss treatment Wegovy and diabetes drug Ozempic, it said

on Monday.

Construction of the plant at Novo's existing main U.S.

manufacturing site in Clayton, North Carolina, will be completed

between 2027 and 2029, and will add 1,000 workers to the 2,500

already employed there, the Danish company said. Novo opened the

site 31 years ago.

Novo told Reuters late last year it was working to increase

its in-house capacity to fill the injection pens - a process

known as fill-finish - at some manufacturing sites in the U.S.

and Europe.

Booming demand for Wegovy in the United States and the 10

other markets where it has so far been launched has propelled

Novo's shares to record highs and the company last year overtook

LVMH to become Europe's most valuable listed company.

But the success has left Novo facing shortages and forced to

limit the number of patients taking the once-weekly injection.

Boosting output of Wegovy has become more urgent since rival

Eli Lilly ( LLY ) launched its own obesity drug Zepbound in the

U.S. in December.

Neither company can produce enough to meet demand. Some

experts predict that sales for obesity treatments could reach

about $150 billion annually by the early 2030s.

Since launching Wegovy in the U.S. in mid-2021, Novo has

spent billions to boost production - much of it at facilities in

its native Denmark but also at other sites including the one in

North Carolina.

In another attempt to grow Novo's manufacturing capacity for

Wegovy, Novo's controlling shareholder Novo Holdings announced

in February that it would buy Catalent ( CTLT ), a large

U.S.-based contract drugmaker that is a subcontractor for making

Wegovy, for $16.5 billion.

Novo Holdings said that after the deal closes, it will sell

three of Catalent's ( CTLT ) fill-finish sites - in Italy, Belgium, and

in the U.S. - onto Novo Nordisk.

Niels Laurbjerg Nielsen, a corporate vice president at Novo

who is in charge of fill-finish manufacturing at the Clayton,

North Carolina facility, said he could not comment on that deal.

In an interview with Reuters, he declined to specify how

many more doses would be produced there once the new fill-finish

factory opened, but said the investment was part of the

company's efforts to reach more patients.

The initial focus would be on producing Wegovy and Ozempic,

although the manufacturing lines could produce other "future"

medicines, he said, without specifying them.