** Viking Therapeutics' VKTX.O shares have more than doubled this year, on track for a third successive year of gains

** Shares of other smaller obesity drug developers such as Structure Therapeutics GPCR.O, Altimmune ALT.O and Amgen AMGN.O are set to end the year in the red

** BMO Capital analysts termed 2024 a "challenging year for obesity trade" - as investors previously got significant returns by banking on names such as VKTX, GPCR and ALT that were entering the weight-loss space

** Brokerage says that while obesity remains an "enormous" long-term revenue opportunity, investors have become more selective and focus on "clearly differentiated" products

** In November, VKTX reported promising data of its oral drug candidate, VK2735, but analysts raised concerns about its ability to mass produce the treatment

** Data from Amgen's closely watched weight-loss drug MariTide failed to impress investors — and wiped off about $7 bln from the company's market cap in November

** Stock has declined 9.5% this year vs a gain of about 10% last year

** Structure Therapeutics' oral obesity drug surpassed Wall Street expectations as it helped patients reduce weight by 6.2% on average in a mid-stage study

** Stock has fallen 34% this year on concerns about competition from Roche's ROG.S oral drug - but mid-stage data in 2025 is expected to be "highly influential" in determining the company's path forward

** Altimmune is down 37% this year after falling 32% in 2023; company has not provided data updates in 2024 for its obesity drug, pemvidutide, which is in late-stage trial

(Reporting by Bhanvi Satija in Bengaluru)

((Bhanvi.Satija@thomsonreuters.com; Outside U.S. +91 9873062788;))