Myostatin inhibitors are the most serious drug-development effort aimed at muscle, and they are also the least like the products on a research vendor's shelf. We read the trial abstracts and the vendor listings to separate the two. This page is not advice to use anything. Vendors label everything here for laboratory research only.
What myostatin is
Myostatin is a protein in the TGF-beta family that acts as a negative regulator of muscle growth. Mice lacking the myostatin gene have a widespread increase in skeletal muscle mass from a combination of larger and more numerous fibers, and a 2002 paper also reports less fat accumulation as those mice age. A 2004 New England Journal of Medicine paper reported a myostatin gene mutation in a child with gross muscle hypertrophy. Those findings are why companies built drugs to block it.
What the human trials measured
Swipe the table sideways to see every column.
| Compound | Who and how long | What was measured | What the abstract reports |
|---|---|---|---|
| Bimagrumab, an antibody that blocks activin type II receptors (2019) | 67 adults with COPD and low muscle mass, 24 weeks | Thigh muscle volume | 5.0% higher at week 24 against 1.3% lower on placebo. Walking distance did not improve. |
| Landogrozumab, a myostatin antibody (2015) | 201 adults aged 75 or older who had fallen in the past year, 24 weeks | Appendicular lean mass | 0.303 kg gain against a 0.123 kg loss on placebo. The authors say it might improve some functional measures and that more studies are needed. Eli Lilly funded it. |
| Domagrozumab, a myostatin antibody (2020) | 120 boys with Duchenne muscular dystrophy, 48 weeks | Four-stair climb time | No significant difference. Muscle volume rose non-significantly, and the authors say efficacy measures did not support a treatment effect. |
| ACE-031, an activin receptor fusion protein (2017) | Boys with Duchenne muscular dystrophy, ascending doses | Safety first | Stopped after the second dosing regimen over nosebleeds and dilated small blood vessels. The abstract reports only trends for lean mass. |
| Apitegromab, SAPPHIRE (2025) | 188 people aged 2 to 21 with spinal muscular atrophy already on other treatment, 12 months | A motor function score | 1.8 points better than placebo for the combined dose groups in ages 2 to 12. The higher dose alone was not significantly different. The sponsor funded it. |
What the results add up to
A larger muscle on a scan and a stronger person are separate questions, and the trials answered them differently. Bimagrumab and landogrozumab raised muscle measures in COPD and in older fallers, and the first did not move walking distance. Domagrozumab moved no function measure in Duchenne. All five trials enrolled people with a disease or at risk of falls, and none that we found tested healthy lifters. ACE-031 shows that a safety problem can end a program regardless of the muscle signal.
Follistatin sits in a different place
Vendor listings describe follistatin as binding myostatin and a related protein called activin. The one human follistatin study we found delivered the gene by a viral vector to six people with inclusion body myositis, and a later commentary in the same journal disputes its functional claims. It says little about a vial of protein. We cover it in our post on follistatin 344 and, for the wider evidence, the best peptides for muscle growth.
What the vendors list
Of the four vendors we review, Peptides for Sale lists the most. It has follistatin 344, ACE-031, and two listings for myostatin itself, one named GDF-8. Core Power Peptides lists follistatin 344. We found nothing myostatin-related in Peptryn's product sitemap () or in American Peptides' (). Myostatin is the protein that limits muscle growth, so a vial of it is a reagent for assays and the opposite of an inhibitor.
The Peptides for Sale ACE-031 listing says the program was stopped after nosebleeds and small dilated blood vessels, and attributes them to off-target binding of two other proteins. That attribution is the vendor's, and we did not check it. It also says a certificate of analysis is available for each batch, as does its follistatin listing, and we have not read one. The site footer describes the products as made for athletes, biohackers and wellness enthusiasts, which sits oddly next to a research-use-only label, and our Peptides for Sale review scores its documentation lower than the other three. The Core Power Peptides follistatin page says a COA is provided and names no lab, and its review lists the other gaps.
Sports status
The Cologne anti-doping laboratory's glossary says WADA has banned myostatin inhibition since 1 January 2008 under group S4, and quotes the list's wording on agents that modify myostatin function. The page quotes the 2018 list, so a tested athlete should read the current one. Our posts on CJC-1295 and ipamorelin and IGF-1 LR3 cover the S2 side.
Frequently asked questions
What is a myostatin inhibitor?
A compound that blocks myostatin or the receptor it signals through. The trials we read used antibodies such as bimagrumab, landogrozumab, domagrozumab and apitegromab, and a receptor fusion protein, ACE-031.
Did myostatin inhibitor trials increase muscle?
Some measured higher muscle volume or lean mass in specific groups, such as 5.0% higher thigh volume with bimagrumab in COPD. Domagrozumab in Duchenne showed no significant effect. None we found tested healthy lifters.
Is a vial of myostatin an inhibitor?
No. Myostatin is the protein that limits muscle growth, per the 2002 paper and the vendor listings. A vial of it is an assay reagent, and the inhibitors are the compounds that block it.