A 38-year-old woman with hypothalamic obesity following brain tumor treatment achieved remarkable 14% weight loss (131 kg to 112.1 kg) over three months using semaglutide at just 0.5 mg weekly. Her condition, triggered by radiotherapy for suprasellar germinoma at age 16, had caused uncontrollable weight gain from 57 kg to 138 kg despite lifestyle efforts, plus type 2 diabetes requiring intensive insulin therapy up to 100 units daily. Body composition analysis confirmed the weight loss was predominantly fat mass while preserving muscle. This case represents a significant breakthrough for hypothalamic obesity, one of medicine's most treatment-resistant conditions. Traditional hypothalamic obesity stems from damage to appetite regulation centers, making patients nearly impervious to conventional weight loss approaches. The dramatic response suggests GLP-1 receptor agonists may bypass damaged hypothalamic circuits by acting on alternative pathways in the brainstem and periphery. While this single case cannot establish efficacy, it opens promising avenues for the thousands suffering from iatrogenic hypothalamic obesity after brain tumor treatment. The preserved muscle mass during rapid weight loss is particularly encouraging, suggesting metabolically healthy fat reduction rather than generalized tissue wasting.