GSK Pays Up to $1 Billion for SiranBio's Weight Loss siRNA Drug

GSK has entered a licensing agreement worth up to approximately $1 billion for an experimental oligonucleotide drug developed by Siran Biotechnology — a deal that gives GSK access to a long-acting siRNA therapy targeting cardiometabolic disease. The therapy is designed to induce weight loss while preserving lean muscle mass, differentiating it from existing weight management treatments that have faced criticism for muscle loss as a side effect alongside fat reduction.

siRNA — short interfering RNA — works by silencing specific genes at the messenger RNA level, preventing the production of proteins that drive disease. The long-acting formulation that SiranBio has developed is designed to require less frequent dosing than current siRNA therapies, which is a significant commercial and compliance advantage in a chronic disease setting where patients require treatment over extended periods. With Siran Biotechnology under its fold, GSK will have access to a long-acting siRNA therapy that could induce weight loss while preserving lean mass, in addition to addressing other weight-related comorbidities. 

The deal lands as competition in the cardiometabolic and obesity therapy space intensifies rapidly. Eli Lilly's Mounjaro and Novo Nordisk's Ozempic have reshaped the commercial landscape of weight management, but their mechanism — GLP-1 receptor agonism — does not address the full spectrum of cardiometabolic risk. A long-acting siRNA approach targeting a different biological pathway offers GSK a scientifically differentiated entry point into one of the most commercially significant therapy areas in modern medicine.