In light of this, several pharmaceutical companies are now working to develop treatments that preserve or even increase muscle mass while reducing weight.

In 2023 Eli Lilly spent nearly $2bn to acquire bimagrumab, a treatment developed by Versanis Bio that inhibits the activity of myostatin, a protein responsible for muscle breakdown. Lilly is currently conducting interim trials on bimagrumab alone and in combination with Wegovy to evaluate its effect on total body weight. The group is also collaborating with the Chinese company Laekna on a similar drug.

Regeneron is testing trevogrumab, an antibody from the same family as bimagrumab, in combination with Wegovy and another treatment, garetosmab. The three-part study, conducted on healthy participants with obesity, measures changes in weight, fat mass, waist circumference, body composition, and thigh muscle volume. Results are expected next year.

Scholar Rock is evaluating the efficacy of apitegromab, an experimental treatment targeting myostatin, in combination with Lilly's Zepbound. Interim trials have shown that this combination preserves lean body mass better than Zepbound alone.

Last year, Roche launched a study on RG6237, a single-dose therapy for overweight individuals. This treatment, known as "latent myostatin," eliminates the inactive form of the protein in the blood. The Swiss group plans to start an interim trial this year, combining RG6237 with its own GLP-1 candidate, CT-388.

Biohaven is testing taldefgrobep alfa, a drug targeting myostatin, in an early trial for obesity. Although the treatment did not improve motor function in patients with spinal muscular atrophy, it helped reduce total fat mass and showed an increase, albeit numerical, in lean mass and bone density compared to placebo. The laboratory plans to accelerate the transition to an intermediate trial in obese patients.

Keros Pharma is developing KER-065, a treatment that acts on both myostatin and activin A proteins. In obese mice, this drug reduced fat mass when administered alone or in combination with semaglutide, the active ingredient in Wegovy and Ozempic. An early trial in obese male patients is underway, with results expected in the first quarter of 2025.

Northstrive Biosciences, a subsidiary of PMGC Holdings formerly known as Elevai Labs, acquired two myostatin-targeting drugs—EL-22 and EL-32—from South Korean company MOA Life Plus last year. Northstrive plans to seek FDA approval to begin human trials this year in combination with GLP-1 treatments.

Veru is betting on enobosarm, an oral drug that targets androgen hormones involved in body development. In an interim study, patients who received enobosarm with Wegovy lost an average of 71% less lean body mass than those treated with Wegovy and a placebo. An advanced-stage study will aim to determine whether the drug improves muscle strength when climbing stairs in patients aged 60 and older.

Canadian biotech company 35Pharma plans to test the safety of its experimental treatment HS235 in an early-stage study. The drug targets activin and GDF ligands, two proteins that play a key role in regulating skeletal muscle, blood, and bone metabolism. Initial results are expected in the second half of 2025.

Finally, Arrowhead Pharmaceuticals is developing two RNA-based obesity drugs—ARO-INHBE and ARO-ALK7—that interfere with fat storage mechanisms. The company plans to evaluate ARO-INHBE in human trials this year, either alone or in combination with Lilly's tirzepatide, the active ingredient in Zepbound and the diabetes treatment Mounjaro.

In May 2024, AstraZeneca entered into an agreement worth up to $80m with the Swiss start-up SixPeaks Bio to develop an antibody targeting activin cell receptors, with the aim of preserving muscle mass during weight loss therapies. The agreement also includes an exclusive option for acquisition by the British laboratory.