RecruitingPhase 4Drug trialJOULE - Metabolic Adaptation to Weight Loss in Response to a Behavioural Lifestyle Program With or Without Semaglutide in Adolescents With ObesityThe Joule MARS study is a single center, randomized, open label clinical trial aiming to explore the metabolic adaptations that occur in response to weight management in adolescents with obesity. Behavioural lifestyle intervention with and without a pharmacological intervention - semaglutide- will be studied. Study participants will be randomized to one of two groups. Group A will follow a behavioral lifestyle program (BLP) alone for 6 months, followed by BLP and treatment with semaglutide for six months. Group B will be enrolled in BLP and semaglutide from baseline to 6 months. The primary research question will assess, in youth aged 12-17 years diagnosed with obesity and enrolled in a weight management program, if the implementation of a BLP together with semaglutide, compared to the implementation of BLP alone for 6 months leads to less adaptive thermogenesis.