Chugai and Roche Target Weight Regain with Novel Muscle-Preserving Obesity Drug

Japanese pharmaceutical company Chugai Pharmaceutical, a subsidiary of Swiss giant Roche, is advancing a novel obesity drug candidate designed to address a critical limitation of current treatments: the tendency for patients to regain weight after stopping medication. According to Nikkei Asia, the company expects to seek regulatory approval for the drug, known as GYM329, as early as 2028.

The drug enters a market experiencing explosive growth. Goldman Sachs Research projects the global obesity drug market will reach $95 billion by 2030, driven largely by GLP-1 receptor agonists like Novo Nordisk's Wegovy and Eli Lilly's Zepbound. These drugs have proven highly effective for weight loss by mimicking gut hormones that suppress appetite and regulate blood sugar. However, they come with a notable drawback: significant loss of muscle mass, which can lower the body's basal metabolic rate and make it easier to regain weight once the medication is discontinued.

GYM329 is a biopharmaceutical treatment that takes a different mechanistic approach. It works by suppressing the activity of specific proteins that cause muscle atrophy, thereby helping patients maintain lean muscle mass during and after weight loss. The theory is that by preserving muscle, the body's energy expenditure remains higher, creating a more stable metabolic environment that helps prevent the rebound weight gain that often follows treatment cessation.

Chugai and Roche are currently conducting clinical trials for GYM329. The studies are designed to monitor changes in both weight and muscle mass, comparing outcomes for patients using GYM329 in combination with existing GLP-1 medications against those using GLP-1 drugs alone. This combination therapy approach suggests the drug is intended to be used alongside, not instead of, current first-line obesity treatments like Wegovy or Zepbound.

The development of GYM329 reflects the broader industry trend of moving beyond simple weight loss to address the long-term sustainability of treatment outcomes. While GLP-1 drugs have revolutionized obesity care, their high cost—often exceeding $1,000 per month—and the need for continuous use to maintain results have raised questions about accessibility and long-term efficacy. A drug that helps patients maintain their results after stopping medication could significantly improve the cost-benefit profile of obesity treatment.

Chugai's involvement in obesity drug development is not new. The company previously collaborated on the development of orforglipron, an oral GLP-1 receptor agonist being developed by Eli Lilly. Lilly's CEO David Ricks has indicated the company hopes to gain approval for orforglipron in the second quarter of 2026. This existing relationship highlights the interconnected nature of pharmaceutical research, where companies often contribute to multiple parallel developments within the same therapeutic area.

The competitive landscape for next-generation obesity treatments is intensifying. Novo Nordisk recently received FDA approval for an oral version of Wegovy and is advancing an experimental drug that mimics hunger-suppressing hormones. Eli Lilly is developing a new drug that mimics the effects of three hormones simultaneously to achieve greater weight loss, alongside its oral treatment orforglipron. These developments indicate that the industry is moving toward more sophisticated, multi-targeted approaches that address not just weight loss, but also the physiological challenges of maintaining it.

GYM329's focus on muscle preservation represents a potentially valuable addition to the obesity treatment toolkit. Current GLP-1 therapies primarily target appetite and glucose metabolism, but the muscle loss they cause can be counterproductive for long-term metabolic health. By specifically addressing this side effect, GYM329 could help patients achieve more sustainable outcomes. The drug's development timeline suggests it will enter the market just as the first wave of GLP-1 drugs are facing patent expirations and increased competition, potentially positioning it as a premium, next-generation option.

The clinical trial results will be crucial in determining whether the theoretical benefits of muscle preservation translate into real-world advantages in weight maintenance. If successful, GYM329 could help establish a new treatment paradigm where obesity management focuses not just on initial weight loss, but on creating a durable metabolic state that persists after treatment ends. This would represent a significant shift from the current model of indefinite medication use, potentially improving both patient outcomes and healthcare system sustainability.