Not yet, outside a trial. The closest result so far comes from apitegromab, an antibody given with tirzepatide to 102 adults. At 24 weeks it left 1.9 kg less lean mass lost than placebo, and total weight loss was similar in both arms [1]. A second antibody, bimagrumab, has two phase 2 trials behind it [2] [3]. Neither drug is approved, and neither can be bought.
The problem both are aimed at is real. Lean mass is lost in proportion to total weight on drugs such as tirzepatide [1]. The muscle loss guide sets out how much goes and what comes back after stopping. The approaches with evidence today are protein and resistance training. A drug would be a third option, and a second prescription.
Apitegromab: lean mass kept, weight loss unchanged
Apitegromab blocks the activation of myostatin, the signal that limits how much muscle the body builds. In the EMBRAZE trial, adults with overweight or obesity all took tirzepatide and were randomized 1:1 to add apitegromab or placebo [1]. At week 24 the apitegromab group had lost 1.9 kg less lean mass than placebo (P = 0.001). The authors describe that as retaining 54.9% of the lean mass that would otherwise have gone.
The part that mattered most was the weight. Total weight loss was similar between the arms, so the lean mass was retained without blunting what tirzepatide took off. Adverse events ran 39 of 51 on apitegromab against 36 of 51 on placebo. The authors call it a proof-of-concept study, and 51 people per arm over 24 weeks can only detect common problems.
Bimagrumab: fat down, lean mass up, and then a combination
Bimagrumab blocks a different target, the activin type II receptor, and blocking that signal stimulates skeletal muscle growth. The first trial gave it alone, with no GLP-1, to 75 adults with type 2 diabetes and a BMI of 28 to 40 [3]. After 48 weeks of monthly infusions, fat mass fell 20.5% (−7.5 kg) against 0.5% on placebo. Lean mass rose 3.6% (1.70 kg, 80% CI 1.1 to 2.3) against a 0.8% fall on placebo, and body weight fell 6.5%.
That is a gain in lean mass while weight fell. Two limits sit beside it. Only 58 of the 75 completed the 48 weeks, and only participants who completed the full regimen were analyzed. Every interval is again 80%.
The larger BELIEVE trial then paired bimagrumab with semaglutide [2]. It randomized 507 adults with obesity across nine groups for 48 weeks. Body weight fell 9.3 kg on the higher bimagrumab dose alone, 14.2 kg on semaglutide 2.4 mg alone, and 17.8 kg on the high-dose combination, against 3.3 kg on placebo. Its primary endpoint was weight, not lean mass, so it answers whether the two drugs add up on the scale. They did. Muscle spasms, diarrhea and acne were the common side effects of bimagrumab.
What none of these trials measured
Lean mass on a DXA scan includes organs and body water alongside skeletal muscle. None of the three trials reports grip strength, walking speed or any measure of physical function. What was preserved is a compartment on a scan, not a demonstrated ability to lift or carry anything. The same gap runs through the field, as the grip strength evidence shows: mass and strength do not always move together.
The people most likely to need a muscle-sparing drug are older adults, and the trade-offs for them are set out in the analysis in older adults. For now the practical answer has not changed, and it starts with food: how much less people eat shows the size of that fall. The broader case on muscle is in what these drugs do to muscle.