ACE-031, also called ramatercept, is a lab-made protein designed to grow muscle by soaking up myostatin, a signal that limits muscle growth. Acceleron Pharma developed it and tested it in healthy women and in boys with Duchenne muscular dystrophy.
It raised lean mass in early trials. But the Duchenne trial was stopped for nosebleeds and dilated blood vessels in the skin, and the program was dropped in 2013. Today it's sold online as a research "peptide," even though it's a large protein, and lab tests suggest the vials don't contain real ACE-031.
- ACE-031 is a large fusion protein (about 77 kDa), not a short peptide. It acts as a decoy receptor that traps myostatin and related signals.
- One injection of 3 mg/kg raised lean mass by 3.3% in healthy women after 29 days.
- A trial in boys with Duchenne muscular dystrophy was stopped for nosebleeds and dilated skin blood vessels. Development ended in 2013.
- In a 2025 lab test, none of 14 black-market ACE-031 products contained ACE-031.
- It's not FDA approved, and WADA bans it by name.
- The effective trial dose for a 70 kg adult was about 210 mg, more than 200 of the 1 mg vials sold online.
| What it is | Fusion protein: activin receptor IIB joined to an antibody (Fc) fragment |
| Size | About 77 kDa (two 343-amino-acid chains) |
| Common vial online | 1 mg |
| Route in trials | Injection under the skin |
| Human trials | Four early trials; program stopped in 2013 |
| FDA status | Not approved |
| In sport | Prohibited at all times, named in WADA S4.3 |
What Is ACE-031?
ACE-031 is built from two parts: the outer, signal-catching section of a muscle receptor called activin receptor type IIB (ActRIIB), and the stem section of a human antibody (IgG1 Fc).[1] The receptor part catches growth-limiting signals in your blood before they reach your muscles. The antibody part keeps the protein in your body longer.
Acceleron Pharma developed it with Shire. Trials were halted in 2011, and the companies ended the program in 2013.[2] Acceleron is now part of Merck.
It's a protein, not a peptide. Each ACE-031 molecule is two chains of 343 amino acids, about 77,000 daltons before sugar groups are added.[3] A protein like this has to be made in living cells, the way antibody drugs are. That's a key reason to doubt cheap vials sold online.
How ACE-031 Works
Myostatin is a growth brake for muscle. ACE-031 works as a decoy: it binds myostatin and other signals that would normally attach to the ActRIIB receptor on muscle cells, so they can't slow muscle growth.[4]
It catches more than myostatin. In mice, a soluble ActRIIB increased muscle mass by up to 60% in 2 weeks, and it still worked, though less strongly, in mice with no myostatin at all, which showed other signals also hold muscle back.[5] That broad reach is likely why it grew muscle so strongly.
What People Use ACE-031 For
- Muscle growth. The main reason people buy it. The human data are a single-dose study in healthy women and a stopped trial in boys with Duchenne.
- Strength and athletic performance. It's banned in sport. No human study measured strength gains.
- Fat loss and bone density. Trials saw trends toward less fat and higher bone density,[1][4] but these were small, short studies.
- Muscle-wasting diseases. Its intended medical use. Development stopped over safety.
The Research Behind ACE-031
| Study | Who | Dose | What they found |
|---|---|---|---|
| Single-dose trial[4] | 48 healthy postmenopausal women | One injection, 0.02 to 3 mg/kg | At 3 mg/kg: lean mass +3.3%, thigh muscle volume +5.1% at day 29 |
| Duchenne trial[1] | 24 boys with Duchenne muscular dystrophy | 0.5 mg/kg every 4 weeks or 1 mg/kg every 2 weeks | Trends toward more lean mass and bone density; walking not significantly better; stopped for bleeding |
| Mouse study[6] | Young mice | 28 days | Leg muscles 26% to 46% heavier |
| Marmoset study[7] | Marmoset monkeys | 3 mg/kg weekly for 14 weeks | More lean mass and larger muscle fibers |
In healthy women, a single injection of 3 mg/kg raised lean body mass by 3.3% and thigh muscle volume by 5.1% after 29 days, compared with placebo. The drug was generally well tolerated, with redness at the injection site. Its half-life was 10 to 15 days.[4]
In boys with Duchenne, ACE-031 caused no serious or severe side effects, but the study was stopped after the second dose group because of nosebleeds and telangiectasias. Walking distance held steady in the treated boys while it dropped in the placebo group, but the difference wasn't statistically significant.[1]
It doesn't always work. In mice with severe spinal muscular atrophy, an ActRIIB decoy barely improved movement and didn't extend survival.[8]
Is ACE-031 Legal?
ACE-031 isn't FDA approved for any use, and its development has ended. It isn't a legal dietary supplement and isn't on the list of substances compounding pharmacies may use.[9] Sellers offer it as a research chemical labeled not for human use.
In sports, it's banned by name. WADA's Prohibited List includes "decoy activin receptors (e.g. ACE-031)" under section S4.3, prohibited at all times.[10]
A related drug did make it to market. Sotatercept (Winrevair) uses activin receptor type IIA instead of IIB and was approved in 2024 for pulmonary arterial hypertension.[14] Nosebleeds and telangiectasias are among its side effects too.[11][14] It's a different molecule and isn't used for muscle growth.
If you want care for muscle loss, a clinician can check for causes and treatments. You can also find a peptide clinic near you.
ACE-031 vs Follistatin
Both block myostatin, so people often compare them:
| ACE-031 | Follistatin | |
|---|---|---|
| What it is | Engineered decoy receptor | Natural protein your body makes |
| What it blocks | Myostatin, activins and other ActRIIB signals | Myostatin and activin |
| Human data | Two published trials; stopped for bleeding | Gene therapy trials only, not injected protein |
| WADA | Banned by name (S4.3) | Banned (S4.3) |
For the follistatin options sold online, see our Follistatin 344 page and our FLGR-242 page.
ACE-031 Dosage
Trial doses, not recommended doses
ACE-031 was stopped for safety reasons and has no approved dose. The numbers below come from the clinical trials. Talk to a licensed clinician before you inject anything.
Trial doses:
- Healthy women: one injection of 0.02 to 3 mg/kg under the skin in the published study. The muscle gains were seen at 3 mg/kg.[4] A second trial in 70 women gave 2 to 7 injections over 1 to 3 months; its results weren't published.[15]
- Boys with Duchenne: 0.5 mg/kg every 4 weeks, or 1 mg/kg every 2 weeks, for 12 weeks. The bleeding problems clustered at 1 mg/kg.[1][12]
What that means in vials: for a 70 kg (154 lb) adult, 3 mg/kg is 210 mg, and 0.5 mg/kg is 35 mg. Online sellers offer 1 mg vials. That's a small fraction of the dose that changed muscle in trials, assuming the vial even contains the right protein.
ACE-031 dosage chart (1 mg vial)
| Dose | Units with 1 mL BAC water |
|---|---|
| 100 mcg | 10 units |
| 500 mcg | 50 units |
| 1 mg | 100 units (the whole vial) |
With 1 mL of bacteriostatic (BAC) water, each unit on a U-100 insulin syringe holds 10 mcg. Use our peptide calculator for other volumes, and the reconstitution guide for mixing steps.
ACE-031 Side Effects
From the clinical trials:[1][4][12]
- Nosebleeds. 5 of 9 boys on 1 mg/kg every 2 weeks, compared with none on placebo
- Telangiectasias (small dilated blood vessels in the skin). Also 5 of 9 boys at that dose, and none on placebo
- Gum bleeding, reported across the trial program[2]
- Redness at the injection site. The main side effect in healthy women
- Headache
The bleeding and blood vessel effects went away after the drug was stopped.[2] Sotatercept, a related drug that traps similar signals, causes similar nosebleeds and telangiectasias.[11]
The fake-product problem. In 2025, an anti-doping lab tested 14 black-market ACE-031 products. Twelve held the full-length receptor protein without the antibody part, so not ACE-031. One held follistatin 344 and one held ipamorelin, a different peptide. The products also contained many other proteins.[13] Injecting an unknown protein mix carries its own risks, including immune reactions and contamination.
Who should avoid it: anyone with a bleeding disorder or on blood thinners, anyone pregnant or breastfeeding, anyone under 18, anyone with cancer or a history of it, and athletes who are drug tested.
Frequently Asked Questions
What is ACE-031? A lab-made decoy receptor protein that traps myostatin and related signals. Development stopped in 2013.
Is ACE-031 a peptide? No. It's a large fusion protein of about 77 kDa.
Does ACE-031 build muscle? One 3 mg/kg dose raised lean mass 3.3% in healthy women. The Duchenne trial was stopped before showing a clear benefit.
Why was ACE-031 discontinued? Nosebleeds and dilated skin blood vessels in the Duchenne trial; follow-up animal studies didn't support going further.
Is the ACE-031 sold online real? A 2025 lab test found none of 14 black-market products contained ACE-031.
What dose of ACE-031 was used in trials? 0.02 to 3 mg/kg once in healthy women in the published study; 0.5 to 1 mg/kg every 2 to 4 weeks in boys with Duchenne.
What are the side effects of ACE-031? Nosebleeds, telangiectasias, gum bleeding, injection site redness and headache.
Is ACE-031 banned in sports? Yes. WADA bans it by name.
What is the difference between ACE-031 and follistatin? ACE-031 is an engineered decoy receptor tested in trials. Follistatin is a natural protein with gene therapy data only.
Is ACE-031 FDA approved? No. The related drug sotatercept is approved for pulmonary arterial hypertension.
References
- Campbell C, McMillan HJ, Mah JK, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: results of a randomized, placebo-controlled clinical trial. Muscle Nerve. 2017;55(4):458-464. PMID: 27462804
- Muscular Dystrophy Association. Update: ACE-031 clinical trials in Duchenne MD. MDA Quest. mda.org
- KEGG DRUG. Ramatercept (D10347). kegg.jp
- Attie KM, Borgstein NG, Yang Y, et al. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve. 2013;47(3):416-423. PMID: 23169607
- Lee SJ, Reed LA, Davies MV, et al. Regulation of muscle growth by multiple ligands signaling through activin type II receptors. Proc Natl Acad Sci U S A. 2005;102(50):18117-18122. PMID: 16330774
- Cadena SM, Tomkinson KN, Monnell TE, et al. Administration of a soluble activin type IIB receptor promotes skeletal muscle growth independent of fiber type. J Appl Physiol (1985). 2010;109(3):635-642. PMID: 20466801
- Cadena SM, et al. ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (Callithrix jacchus). PLoS One. 2026;21(2):e0342666. PMID: 41686840
- Sumner CJ, Wee CD, Warsing LC, et al. Inhibition of myostatin does not ameliorate disease features of severe spinal muscular atrophy mice. Hum Mol Genet. 2009;18(17):3145-3152. PMID: 19477958
- U.S. Food and Drug Administration. Bulk drug substances nominated for use in compounding under section 503A. Updated May 14, 2026. fda.gov
- World Anti-Doping Agency. The 2026 Prohibited List, section S4.3. wada-ama.org
- Hoeper MM, Badesch DB, Ghofrani HA, et al. Phase 3 trial of sotatercept for treatment of pulmonary arterial hypertension. N Engl J Med. 2023;388(16):1478-1490. PMID: 36877098
- ClinicalTrials.gov. A phase 2 study of ACE-031 in subjects with Duchenne muscular dystrophy (NCT01099761), posted results. clinicaltrials.gov
- Reichel C, et al. Gel electrophoretic detection of black market ACE-031. Drug Test Anal. 2025;17(10):1934-1946. PMID: 40312924
- U.S. Food and Drug Administration. Winrevair (sotatercept-csrk) prescribing information. 2024. fda.gov
- ClinicalTrials.gov. A safety, tolerability, pharmacokinetic and pharmacodynamic study of ACE-031 in healthy postmenopausal women (NCT00952887). clinicaltrials.gov
This information is for educational purposes only and does not constitute medical advice. Always consult a qualified healthcare provider before starting any peptide therapy. Regulatory status may change.
