GYM329 dosage and evidence
Written by Aaron CuhaReviewed Sep 2026
The short answer
GYM329 is the one myostatin antibody now being tested where it matters most for readers. One study pairs it with tirzepatide in people with obesity. Another tests how well the body uses insulin in type 2 diabetes. No results yet.
Evidence grade for GYM329: Preliminary. The rule: studied in people, but no published study has had people take it. The sum on this page: 2 human studies where nobody was given it, 1 registered with no result. A grade counts how much has been done to people, not whether it works.
- People given it
- 0
- Human studies
- 0
- Found nothing
- 0
Dose
No human dose established
No published study on this page has given this compound to people and reported a result.
2 human studies where nobody was given it, 1 registered with no result
1 effects reported, 1 unwanted, by people using it, not a trial
Goal pages: Fat loss and metabolism, Muscle and strength
In plain English
In plain English, from Aaron
This is how I would explain it to a friend. The evidence, with the numbers, is further down the page.
GYM329 is a lab-made antibody that blocks myostatin, the body's brake on muscle growth. Chugai and Roche built it to clear myostatin out of the body, not just block it. It is being tested with the weight loss drug tirzepatide. The question is whether it can save the muscle people lose on these drugs. It is not approved, and no results are out.
What people take it for
- Keeping muscle while losing weight on a GLP-1 drug.
- Better blood sugar control by adding muscle.
- Muscle in spinal muscular atrophy.
What studies in people showed
No results in people have been published. A study in 285 people with obesity is testing it with tirzepatide. It is no longer taking new people. Another study is testing blood sugar control and muscle in type 2 diabetes. A third is in spinal muscular atrophy. It finished in early 2023 and nothing has been posted. The only published work is in mice and in a dish. In mice with muscle disease, it made muscles stronger. Three earlier drugs like this also looked good in animals. In people, they added muscle without adding strength.
What people report
Reports, not study results
The good
- We have not collected user reports on this one yet.
The bad
- No results in people have been posted, so its side effects in people are not known.
Where these come from: There are no user reports or human results on this page to draw from.
My bottom line
This is the one to watch if you are on a GLP-1 drug and worried about losing muscle. But no result is out, and three drugs like it added muscle without adding strength. In my opinion, lift and eat your protein now. Those have real study support, and you do not need to wait.
An opinion, not a finding. I am a coach, not a doctor.
What it has been measured to do
Measured in people
Goals GYM329 has been tested for in people, biggest studies first. We count only what the studies on this page say, so the real numbers may be higher.
- Blood sugar and insulinno headcount stated · 1 study
Animal and lab work, not yet tested in people
Real results, but from animals or cells, not people. What works in a mouse often does not work the same way in a person. Nobody can patent this, so nobody would ever earn back the cost of a study in people. That is usually why there is none. The record on this one is set out below.
- Getting stronger1 animal or lab study
34 of the 36 indexed goals have no study of any kind behind GYM329
No study in people, animals or cells on this page reports a result for these. That does not prove GYM329 does nothing for them. It does mean anything you have heard about GYM329 and one of these did not come from a study cited here.
Show full evidence
What is GYM329?
GYM329 is the one myostatin antibody now being tested where it matters most for readers. One study pairs it with tirzepatide in people with obesity. Another tests how well the body uses insulin in type 2 diabetes. No results yet.
Three myostatin-blocking antibodies added lean mass and failed to improve function. All three were tested in people with muscular dystrophy or long-term weakness. GYM329 is the first aimed squarely at the kind of people who read this site. That makes it the biggest open question in the field.
Two things set it apart. First, the design. It targets the stored, inactive form of myostatin (latent myostatin). It is also built to sweep its target out of the body, rather than just block it. Second, who it is being tested in. One study looks at how well the body uses insulin, and at muscle makeup, in type 2 diabetes with overweight or obesity. Another pairs it with tirzepatide in 285 people with obesity.
No results in people have been published. This page exists so that when they arrive, you already know what three earlier antibodies did and did not do.
How does GYM329 work?
Chugai and Roche built this antibody to grab latent myostatin, the stored, inactive form, instead of the active form. It uses a design called antigen sweeping. The antibody and its target get pulled into cells and broken down, so the target is cleared rather than just blocked. The stated goal is deeper, longer-lasting blocking than earlier antibodies managed. That is the same reasoning behind domagrozumab's higher doses, and it did not work there.
What have studies in people found about GYM329?
No published results in people. Studies are registered in the groups that matter most for this site's main question, and none has reported.
- A mid-stage study pairing it with tirzepatide, in 285 people with obesity or overweight and at least one weight-related health problem, is under way. It is no longer taking new people.
- A study in type 2 diabetes with overweight or obesity is looking at how well the body uses insulin and at muscle makeup. That is the protect-your-muscle idea, stated outright.
- A study in spinal muscular atrophy runs alongside the drug risdiplam.
- Everything published so far is animal and lab work: mouse disease models reporting stronger muscles, plus a lab safety check.
What this does not tell you: Everything published about this antibody is animal work. The mouse result showing stronger muscles would matter most if it carries over to people. Carrying over is exactly what the three earlier antibodies failed to do, after similarly hopeful animal work. Treat the tirzepatide study as the real test, not the animal data as the answer. No results are posted for any of these studies.
The state of the research
Look at all the myostatin blockers together and one result repeats. Blocking myostatin reliably adds lean mass, by roughly a quarter to half a kilogram in the studies that measured it well. And it reliably fails to improve what a person can actually do. Stamulumab found no gain in strength or function. Domagrozumab missed its main goal and every other clinical measure it checked. Landogrozumab added 0.43 kg of arm and leg lean mass, a very clear result, and moved two of about seven movement tests. Bimagrumab, which this site covers on its own page, made the biggest change in body makeup in the group, and it did not bring a matching gain in function either. The muscle shows up. The ability does not follow.
GYM329 is why that pattern is not the end of the story. Every failed study in this class was run in people with damaged or long-weakened muscle. There, taking the brake off growth may just be the wrong lever. Nobody has tested it in the situation readers of this site actually face. That is fast weight loss on a GLP-1 type drug, taking lean tissue along with the fat. That study now exists and has not reported. When it does, ask the same question the earlier studies answered badly. Did anyone become able to do something they could not do before?
The evidence, in charts
Fig. 1a · how many people
3studies in people cited, but none says how many people took part
number of people not stated
We do not draw a total, because none of the studies in people on this page gives one. Read the sources below for what each study measured.
We read the number of people from the source lines on this page. Where a line gives no number, we count nothing for it. We do not guess.
Fig. 1b · evidence mix
3 of 5 sources here are studies in people. The rest are not.
- Study in people · done in people360%
- Animal study · done in animals120%
- Lab (cells in a dish) · cells or tissue120%
Counted from the list of sources on this page. It counts only what we cite, so there may be more studies out there. A review counts once, however many studies it sums up.
Fig. 2 · evidence over time
The studies cover 4 different years, 2021 to 2026, counted from the list of sources on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Not approved
AU
Not approved
CA
Not approved
Not approved in any of the four countries shown. This is what the law says, not a verdict on the science. See Legal status below for the full text and any notes.
Fig. 4 · how much does what
Nobody has tested different amounts in people
This chart would show how the effect changes as the amount goes up. For this compound, nobody has measured that in people. So we leave it empty. We will not borrow an animal chart and pretend it works the same in people.
Fig. 5 · what the molecule is
- Kind of compound
- Biologic
- Molecule weight
- Engineered monoclonal antibody, roughly 150 kDa. Not a peptide.
- Half-life
- Stated in words, not a numbersee the exact wording below
- Chain length
- None on file
Half-life as stated on file: Not asserted. No human half-life figure was resolved in the sources loaded.
No amino acid sequence is on file for GYM329, so none is drawn rather than guessed from a name.
The studies we cite
- Study in people2026A study to assess efficacy, safety, tolerability, pharmacokinetics and pharmacodynamics of RO7204239 in combination with tirzepatide in participants with obesity or overweight with at least one weight-related comorbidity
This is the trial that matters most to anyone losing weight on a GLP-1 drug, and it has not reported yet. 285 people with obesity are taking tirzepatide with or without a myostatin blocker. The question is whether blocking myostatin saves the muscle that rapid weight loss takes with it. Enrolment is closed and the trial is still running. Nothing has been published. Until it reports, the idea that these drugs protect muscle is an idea, not a finding.
Phase 2, 285 participants, active and not recruiting. The trial that tests whether blocking myostatin preserves what a GLP-1 drug takes. This is the single most relevant registered study to the muscle-loss question on this site.
- Study in people2026A study of GYM329 for insulin sensitivity and muscle composition in type 2 diabetes with overweight or obesity
Nobody has shown that a myostatin blocker improves blood sugar control in people. This trial is testing it in adults with type 2 diabetes who also carry extra weight. The reasoning is that muscle is where most of your blood sugar goes after a meal, so more muscle should mean better control. That chain has never been demonstrated with one of these drugs. Enrolment is closed and the trial is still running. No results have been posted.
The metabolic indication. Muscle is the main site of insulin-stimulated glucose disposal, so more muscle should improve insulin sensitivity. That chain has not been demonstrated with a myostatin antibody in humans.
- Study in people2024A study of RO7204239 in participants with spinal muscular atrophy
This trial took the same antibody back to a nerve and muscle disease, and it has published nothing. People with spinal muscular atrophy took it alongside risdiplam. The trial finished in early 2023. No results have been posted on the registry and no paper has appeared. This is the population closest to the two earlier antibodies, both of which failed. Silence for years after a trial completes is worth noticing on its own.
The neuromuscular indication, run alongside risdiplam. The population closest to where the earlier antibodies were tested and failed.
- Animal study2021Novel myostatin-specific antibody enhances muscle strength in muscle disease models
In mice. In mouse models of muscle disease, this antibody made muscles stronger. That matters because strength is exactly what the three earlier antibodies failed to improve in people. The earlier antibodies also looked hopeful in animals first.
The preclinical characterisation. Mouse disease models. Reports enhanced muscle strength, which is notable precisely because that is the endpoint the three earlier antibodies failed to move in humans. Animal work, and the site keeps that separate from human evidence for exactly this reason.
- Lab (cells in a dish)2023Preclinical in vitro evaluation of immune suppression induced by GYM329, Fc-engineered sweeping antibody
In a dish. This lab study looked at how the antibody's sweeping design affects immune cells. The same design that sets GYM329 apart also engages immune cells, and this study measured how much it turns the immune system down. That is a safety question the earlier antibodies did not have.
In vitro. Worth reading for what it is about rather than as a routine safety box: the antigen-sweeping Fc engineering that makes this antibody clear its target also engages immune cells, and this study evaluates the resulting immune suppression. The mechanism that differentiates GYM329 from the antibodies that failed is also the mechanism that creates a safety question the others did not have.
Common questions
Has GYM329 been tested in people?
Not in a completed trial cited here. 2 human studies where nobody was given it, 1 registered with no result. GYM329 is the one myostatin antibody now being tested where it matters most for readers. One study pairs it with tirzepatide in people with obesity. Another tests how well the body uses insulin in type 2 diabetes. No results yet.
What is the GYM329 dosage?
No human dose established. No published study on this page has given this compound to people and reported a result. 2 human studies where nobody was given it, 1 registered with no result
Is GYM329 FDA-approved?
Investigational. Not approved for any use.
Is this the drug that stops muscle loss on GLP-1s?
It is the drug being tested for that, alongside tirzepatide in 285 people. No results are published. Three earlier antibodies in this class added lean mass without improving function. So the result worth waiting for is about what people can do, not just a body scan.
How is it different from the antibodies that failed?
It targets latent myostatin, the stored inactive form. It also sweeps the target out of the body rather than only blocking it. The aim is deeper, longer-lasting blocking. But domagrozumab was also stronger than the one before it, and that did not help. So strength of blocking alone has already failed once as the answer.
Can I get it?
No. It is still being tested and is not approved anywhere. The only way to get it is in a clinical study.
What should I do about muscle loss on a GLP-1 in the meantime?
The things with real study support are strength training and enough protein. Neither needs you to wait for this antibody. The training and diet sections of this site cover what has been measured for both.