Pharmaceutical companies are racing to develop drugs that prevent muscle loss during weight reduction, addressing a critical side effect of GLP-1 medications like Ozempic and Zepbound. While current weight-loss drugs often cause patients to lose significant lean mass alongside fat, new candidates—including bimagrumab and Cambrian Biotech’s ATX-304—aim to prioritize metabolic health and muscle preservation, according to industry reports and recent clinical data.
Why is muscle loss a concern with current weight-loss drugs?
Rapid weight loss frequently triggers the body to burn muscle for energy, a process that can lead to frailty and weakened bones. According to research cited by Versanis founder Lloyd Klickstein, traditional weight loss typically consists of 65% to 75% fat and 25% to 35% lean mass. When patients use GLP-1 agonists, the resulting appetite suppression can make it difficult to consume enough protein to maintain muscle growth, creating a clinical challenge for physicians monitoring patients for metabolic disease.
What are the leading muscle-preserving drug candidates?
Biotech firms are increasingly repurposing failed drugs to address the metabolic role of muscle. Eli Lilly acquired bimagrumab from Versanis in 2023; the drug, originally developed by Novartis for age-related muscle loss, recently showed in a 500-person study that participants lost over 90% body fat when combined with an Ozempic prescription, according to company data.
Other firms are targeting different mechanisms:
- CagriSema: Novo Nordisk’s combination of Ozempic and cagrilintide, which trials indicate achieved 67% fat loss.
- SPX-001: A candidate acquired by AstraZeneca in 2025 specifically designed to preserve lean mass.
- ATX-304: A Cambrian Biotech pill that mimics the metabolic effects of exercise. In a small safety trial of 23 adults, it increased resting metabolic rate and reduced visceral fat.
How do these new drugs differ from exercise?
Unlike GLP-1 drugs that primarily dampen appetite, candidates like Cambrian Biotech’s ATX-304 are designed to turn up the body’s caloric burn. Cambrian CEO James Peyer told Business Insider the drug aims to make fat metabolically active and force muscles to burn more energy, effectively mimicking the metabolic output of a 5-10k run without physical exertion.
However, the industry faces a hurdle regarding regulatory approval. Endocrinologist Daniel Drucker of the University of Toronto notes that because no regulatory pathway currently exists for “body composition changes,” companies must prove these drugs prevent clinically significant events like falls or fractures to gain FDA approval and insurance coverage.
Frequently Asked Questions
Are these drugs currently available?
No. Most of these candidates are in various stages of clinical trials. The next major data readout for Cambrian Biotech’s ATX-304 is expected at the end of 2027.
Can these drugs replace the gym?
While the goal is to mimic metabolic benefits, medical experts like Daniel Drucker emphasize that there is no substitute for the systemic health benefits of traditional exercise, and these drugs have yet to prove they can improve strength or walking speed in clinical settings.
What is the biggest risk of current weight-loss drugs?
The primary concern is the loss of lean mass, which can lead to frailty. This is particularly dangerous for aging populations who are already at risk for bone fractures and loss of mobility.
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