UPDATE 1-Risk of patient overlap between Wegovy and Saxenda obesity drugs, Novo says

* Risk of some cannibalisation between Wegovy, Saxenda

* New study data shows sustained weight loss over 2 years

* Novo will launch Wegovy in the U.S. on June 10

* Shares up 0.56% (Adds details, results from unpublished trial study, analyst comment, share reaction)

COPENHAGEN, June 7 (Reuters) - Novo Nordisk’s new obesity drug Wegovy, far more efficient at causing weight loss in patients than similar drugs on the market, could capture sales of its existing obesity treatment Saxenda in the United States, the firm said on Monday.

A 2.4 milligram dosage of Novo Nordisk’s semaglutide drug was approved by the U.S. Food and Drug Administration (FDA) on Friday under the name Wegovy, and will be launched on June 10.

Shares in Novo Nordisk traded up 0.56% at 0828 GMT.

Semaglutide belongs to a range of new diabetes and obesity drugs known as GLP-1 analogues, which by imitating a gut hormone that stimulates insulin production, lower appetite and increase feelings of fullness in patients.

Novo already has one GLP-1 obesity drug on the market, Saxenda, launched in 2015, but with the introduction of Wegovy to the U.S. market, an overlap between patients could occur, it said.

“There is of course a risk of some cannibalisation between Wegovy and Saxenda and lower initial value per script, while we build the access for Wegovy,” Novo’s executive vice president of commercial strategy, Camilla Sylvest, told an investor briefing.

“Our focus is to start new patients on Wegovy rather than switching patients currently benefiting from Saxenda,” Sylvest added.

Unpublished data from a new trial study called STEP 5 showed treatment with Wegovy over almost two years led to an average weight loss of 17%, with 40% of patients losing 20% or more of body weight, Novo said on Monday.

Sydbank analyst Soren Lontoft Hansen estimated that Wegovy as a “best in class” drug would be able to open a “potentially very attractive”, yet undeveloped obesity drug market.

“Going forward, we expect the obesity market - with the prospect of more innovation being introduced - will grow much faster than Novo Nordisk’s other businesses,” Hansen, who has a “buy” rating on Novo, said.

Novo also said Wegovy, a once-weekly injectable, would be launched at similar list prices in the United States as Saxenda.

Reporting by Nikolaj Skydsgaard, editing by Louise Heavens, Kirsten Donovan