Quick Answer
Bimagrumab is an experimental drug from Novartis. It does something unusual: it helps you lose fat while gaining muscle.
Most weight loss drugs — including GLP-1s like Ozempic, Wegovy, and Zepbound — cause both fat and muscle loss. Bimagrumab works through a completely different mechanism. It blocks a pathway that normally limits muscle growth.
Early clinical trials pairing bimagrumab with semaglutide (the drug in Ozempic and Wegovy) showed better fat loss and better muscle preservation than semaglutide alone.
It is not FDA-approved. It is still in clinical trials. But it may eventually change how GLP-1 treatment works.
The Problem: Muscle Loss on GLP-1s
When you lose weight — any way — you typically lose some muscle along with fat. With GLP-1 medications, this can be significant.
Studies suggest that 25-40% of weight lost on GLP-1 drugs may be lean muscle, not just fat. This matters because:
- Muscle burns more calories at rest
- Less muscle can slow your metabolism
- Muscle loss can make you weaker and more tired
- Regaining weight after stopping GLP-1s often brings back fat, not muscle
This is sometimes called "Ozempic body" — people lose weight but feel weaker or look different than they expected.
Eating enough protein and strength training help. But they do not fully prevent muscle loss for most people on GLP-1s.
How Bimagrumab Works
Bimagrumab is not a GLP-1 drug. It works in a completely different way.
Your body has natural brakes on muscle growth. One of the main brakes is a system called activin receptor type II (ActRII). Myostatin and activins — proteins in your body — bind to this receptor and tell your muscles to stop growing.
Bimagrumab is a monoclonal antibody that blocks ActRII. When this receptor is blocked:
- Your muscles receive fewer "stop growing" signals
- Muscle tissue grows or is maintained even when you are eating less
- Fat loss can continue independently
Think of it like this: GLP-1 drugs reduce how much you eat. Bimagrumab tells your muscles to hold on while you are eating less.
What the Trials Show
Bimagrumab Alone
A 2021 study published in JAMA Network Open looked at bimagrumab alone in adults with obesity and type 2 diabetes.
After 48 weeks:
- Fat mass decreased by about 20.5%
- Lean muscle mass increased by about 3.6%
- Total body weight decreased by about 6.5%
That combination — fat down, muscle up — is rare. Most weight loss interventions cause both to drop.
Bimagrumab + Semaglutide
More recent data looked at combining bimagrumab with semaglutide (the drug in Ozempic/Wegovy). The combination outperformed semaglutide alone:
| Outcome | Semaglutide alone | Bimagrumab + Semaglutide |
|---|---|---|
| Fat mass loss | ~12-14% | Higher |
| Lean muscle mass | Slight decrease | Preserved or increased |
| Total weight loss | ~15% | Similar or slightly higher |
The exact numbers vary by study and dose. The key finding is that adding bimagrumab appears to shift what kind of weight you lose — more fat, less muscle.
Current Status
As of 2026, bimagrumab is in Phase 2 clinical trials. Novartis is studying it in combination with GLP-1 drugs for obesity treatment.
Phase 2 means:
- The drug has been shown to be safe enough to test in larger groups
- Researchers are working out the best doses and combinations
- Results from Phase 2 inform whether Phase 3 (larger, longer trials) happens
- FDA approval is likely several years away even if everything goes well
How Is This Different From Just Lifting Weights?
Strength training is still the best tool most people have for preserving muscle during weight loss. Protein intake also matters a lot.
Bimagrumab is not a replacement for either. But it may help in cases where:
- Someone cannot exercise much due to injury or health issues
- Muscle loss is happening faster than exercise can compensate
- Someone wants to maximize fat loss without the usual trade-offs
It is also worth noting: some people on GLP-1 drugs lose so much appetite that eating enough protein becomes hard. Bimagrumab could theoretically help fill that gap.
What You Can Do Now
Bimagrumab is not available yet. But you can take steps today to reduce muscle loss on GLP-1 drugs:
- Hit your protein target — aim for at least 0.7-1g of protein per pound of goal body weight
- Strength train 2-3 times per week — even light resistance work helps
- Do not crash your calories — extreme restriction speeds muscle loss
- Keep your protein high even when nausea hits — protein shakes and Greek yogurt are easy options
For more on this topic, see our guide to preventing muscle loss on GLP-1s.
The Bottom Line
Bimagrumab is one of the more interesting drugs in the pipeline. It targets something GLP-1 medications do not: muscle preservation.
If you have worried about losing muscle on Ozempic or Wegovy, bimagrumab is the drug worth watching. The early data is genuinely promising.
But it is years from being available. For now, protein and strength training are your best tools.
This article is for informational purposes only and does not constitute medical advice. Talk to your healthcare provider before starting or changing any medication. Individual results vary. Clinical data cited is from early-phase trials and subject to change.