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Lexicon
Muscle & performance

ACE-031

A myostatin and activin trap that blocks the muscle's natural growth brake, but clinically stopped due to side effects.

3 min read 5 sources

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ACE-031 vial with white powder and the black TPD label on a white podium, next to it two large blue protein models made of many spheres in a bright lab
Phase 2, development stopped · not approved

Summary

At a glance

Sources checked on 26 Oct 2026

Lean mass after one dose
+3.3 %

day 29, highest study dose, healthy postmenopausal women1

Thigh muscle volume
+5.1 %

measured by MRI, same group1

Half-life
10 to 15 days

mean across doses, large fusion protein1

New trials since 2011
0 trials

both phase 2 trials terminated early, as of 26 Oct 20264

  • ACE-031 (ramatercept) is a large fusion protein made of the activin receptor IIB and an antibody piece. It traps myostatin and related messengers that brake muscle growth.15
  • After a single dose lean mass in healthy women rose by 3.3 percent and thigh muscle volume by 5.1 percent, each in the group with the highest study dose.1
  • In boys with Duchenne muscular dystrophy the trial was stopped early: nosebleeds and widened small blood vessels (telangiectasias) were the deciding factors.2
  • In marmoset monkeys muscle mass and strength also increased. There was never an approval, development has been dormant since 2011.34
  • Everything here is the state of research, not a recommendation.4
Profile

Updated May 2026

Class
ActRIIB-Fc

myostatin/activin trap

Use
Subcutaneous

no established protocol

Half-life
long

fusion protein

Status
Development stopped
Sizes
1 mg

1 size in the shop

Contents 16 sections
  1. At a glance
  2. What is ACE-031?
  3. How it works
  4. What you need
  5. Reconstitution
  6. Dosing
  7. Injection
  8. What the research shows
  9. Research status
  10. Side effects
  11. Practice
  12. Storage
  13. Related compounds
  14. FAQ
  15. Glossary
  16. Sources

What is ACE-031?

ACE-031 (ramatercept) is a fusion protein that mimics part of the activin receptor IIB and so traps myostatin and related messengers before they take effect. Myostatin is the muscle's natural growth brake, ACE-031 releases that brake.

Important: ACE-031 is not a small peptide but a large protein that was dosed in mg per kilogram of body weight. Clinical development was stopped due to side effects.

Comparison

Myostatin in the lexicon

Which entries relate to myostatin and which take a different route to muscle, as stated in the TPD lexicon. Tap a card to open its entry.

Myostatin trap (protein) ACE-031 MSTN
Myostatin itself, lab reagent GDF-8 (Myostatin) MSTN Steroid derivative, said to lower myostatin YK11 MSTN Different route via IGF-1 IGF-1 LR3 IGF-1R

Simplified: ACE-031 traps myostatin, GDF-8 is myostatin itself, IGF-1 variants act via their own receptor. 51

How it works

Normally myostatin brakes muscle growth via the ActRIIB receptor. ACE-031 acts like a trap: it catches myostatin and related activins so the braking signal does not reach the receptor. The result in studies was a gain in lean mass.

The catch: the ActRIIB receptor controls not only muscle but also blood vessels, hence the problematic side effects.

Where it acts

Where ACE-031 acted in studies

Tap a point or a card. Colour = myostatin, grey = observed in studies.

  1. Skeletal muscle

    Myostatin trapped, lean mass +3.3% and thigh muscle +5.1% after one dose1

    MSTN
  2. Blood vessels

    Nosebleeds and widened small vessels, reason the trial was stopped2

    Observed in trials
  3. Bone

    Blood markers suggest more bone formation, in Duchenne a trend to higher bone density1

    Observed in trials
  4. Fat tissue

    Trend to less fat mass in Duchenne, not significant2

    Observed in trials
  5. Skin

    Redness at the injection site as the most common reaction after one dose1

    Observed in trials

Targets in the ChEMBL database5

Compound CHEMBL2108674: one recorded mechanism, Inhibitor, traps the messenger.

Myostatin (GDF-8)
Gene
MSTN
UniProt
O14793
ChEMBL
CHEMBL3407325
Action
Inhibitor, traps the messenger
Transparent muscle fibres with docking sites, on them blue two-lobed glass shapes holding dark spheres, above them blue protein models made of many spheres
ACE-031 traps myostatin before it can brake muscle. Symbolic image.

What you need

Supplies

2 things, numbered as in the picture

Tick off what you already have. Vial and BAC water are our real shop photos at the same size.

ACE-031 vial and bacteriostatic water at the same size with the dark TPD label and blue caps, next to them two insulin syringes, two alcohol swabs and a sharps container with a blue lid

  1. ACE-031 vial

    The ACE-031 vial (lyophilized powder).

    In the shop

  2. Water and supplies

    Bacteriostatic water, insulin syringes, alcohol swabs.

    In the shop

Reconstitution

Use the peptide calculator for concentration and volume. But note: in the studies ACE-031 was dosed in mg per kilogram of body weight, in far higher amounts than small vials provide. For research use there is no established, safe protocol.

Step by step

Dissolving the powder

Four steps, the same for every vial size.

  1. 1Wipe the cap

    Clean the rubber stopper with an alcohol swab.

  2. 2Add BAC water

    Just add it, it does not matter if it hits the powder directly.

  3. 3Swirl or shake

    Until everything has dissolved, both are fine.

  4. 4Draw up

    With the U-100 insulin syringe.

Less water higher concentration fewer units on the syringe Example: 1 mg + 1 ml = 1 mg/ml

Dosing

Dosing

Dosing, titration and syringe

Loading the dosing information …

  • Getting started and stepping up, drawn as a staircase
  • Units on the U-100 syringe for every step
  • How long one vial lasts

Injection

ACE-031 was given subcutaneously in the studies. Lacking an established protocol and given the safety record, particular restraint is warranted here.

The injection is subcutaneous, into the fat layer under the skin. Common spots are the abdomen (keep about two finger-widths clear of the navel), the front and the inner side of the thigh, or the back of the upper arm.

The short version:

Injection

Where and at what angle

Pick a spot or switch the angle. Subcutaneous means: into the fat layer, not the muscle.

Rotate the spot each time, never the same one twice in a row.

90°More fat under the skin

Rule of thumb: where there is more fat under the skin, insert straight at 90 degrees. In lean people with little fat, 45 degrees, so the needle stays in the fat layer. Simplified diagram.

  1. Clean the spot with an alcohol swab and let it dry

  2. Pinch up a small fold of skin

  3. Insert the needle: at 90 degrees where there is more fat under the skin, at 45 degrees in lean people with little fat

  4. Inject slowly, wait a moment, then withdraw

  5. Put the needle straight into the sharps container

Rotate the site each time so the tissue does not get irritated. Never the same spot twice in a row.

What the research shows

A phase 1 study (Attie, 2013) showed a dose-dependent rise in lean mass in healthy women, so ACE-031 works. But a study in boys with Duchenne muscular dystrophy (Campbell, 2017) was stopped early after side effects like nosebleeds, gum bleeding and dilated blood vessels appeared.

These vascular side effects are why ACE-031 never reached approval. That should be known before even considering it.

Study results

What the trials measured

Interactive: switch tabs, tap points, show or hide arms. Arms are named relative to each other, no dosing advice.

Muscle after a single dose1

Change at day 29 from baseline, given under the skin

Total lean mass1 measured by DXA
Highest study dose 3.3%
Thigh muscle volume1 measured by MRI
Highest study dose 5.1%

48 healthy postmenopausal women, one dose at ascending levels or placebo. The rise was significant only in the group with the highest study dose. Blood markers suggested changes in bone and fat metabolism as well.

Glass sculpture of a thigh muscle and a thigh bone on a round glass base, surrounded by bright light trails
Studies measured muscle, bone and fat. Symbolic image.

Research status

Where the research stands

ClinicalTrials.gov lists four trials with ACE-031, all from 2008 to 2011. Both phase 2 trials were terminated early, no new trial has been added since. As of 26 Oct 2026. 4

  1. Preclinical Mice and marmosets: more muscle mass and strength
  2. Phase 1 2 trials, 2 completed
  3. Phase 2 2 trials, 0 completed, 2 stopped early
  4. Phase 3 no registered trial
  5. Approval not yet
Not approved. ChEMBL lists ramatercept with phase 2 as the highest phase, clinical development was stopped.4
Show all 2 phase 2 trials on a timelineHide timeline 0 completed 0 running 2 stopped early 1 with results
Phase 2

Bar: start to primary endpoint (planned for running trials). Green = completed, blue = progress until 26 Oct 2026, grey = stopped early. Phase 1: 2 trials on safety and pharmacokinetics, not shown as bars.

Side effects

  • Nosebleeds and gum bleeding.
  • Dilated small blood vessels (telangiectasia) on the skin.
  • These vascular effects led to the stop of clinical development.

Practice

  1. Development was stopped for safety reasons, the clearest signal there is.

  2. No established, safe dosing protocol.

  3. Banned in official competition.

Two light blue dumbbells, a glass of water and a bowl of salad with broccoli, tomatoes and carrots on a bright table

Storage

Before mixing the powder is robust, normal room temperature (around 20 to 25 degrees) is fine, ideally kept in the dark. After mixing, keep in the fridge (2 to 8 degrees), do not freeze. It stays good there for at least 4 to 6 months with barely any loss of potency, in practice considerably longer. Swirl or shake to mix, both are fine.

Shelf life

How long it keeps

Undissolved (powder) Room temperature, around 20 to 25 degrees, dark

Robust, no fridge needed.

Dissolved (mixed) Fridge, 2 to 8 degrees, do not freeze

At least 4 to 6 months with barely any loss of potency. Swirling or shaking to mix are both fine.

  • Keep it dark
  • Dissolved: 2 to 8 degrees
  • Note the mixing date on the vial
Nine vials with white powder and blue caps in the door shelf of a bright fridge
Powder dark at room temperature, once dissolved into the fridge (2 to 8 degrees), stable there for at least 4 to 6 months. Symbolic image.

Related

Related compounds

Same targets or a different path: all in the TPD lexicon.

ACE-031
GDF-8 (Myostatin) Myostatin itself, which ACE-031 traps YK11 Described as a myostatin inhibitor, very thin data IGF-1 LR3 Different route to muscle growth MGF (Mechano Growth Factor) IGF-1 variant from muscle, purely preclinical

FAQ

Common questions about ACE-031

Short answers, each backed by the sources below.

What is ACE-031?

A large fusion protein: the outer part of the activin receptor IIB, linked to a piece of an antibody (IgG1 Fc). It binds myostatin and related messengers in the blood before they reach the receptor on muscle. The compound name is ramatercept.25

What did the first human study show?

48 healthy postmenopausal women received a single dose at ascending levels or placebo. In the group with the highest study dose lean mass rose by 3.3 percent and thigh muscle volume by 5.1 percent after 29 days. The half-life was 10 to 15 days.1

Why was development stopped?

In the trial in boys with Duchenne muscular dystrophy nosebleeds and telangiectasias occurred, meaning widened small blood vessels. The trial was stopped after the second dosing regimen because of potential safety concerns. The activin receptor IIB acts not only on muscle but also on vessels.2

Was there a benefit in Duchenne?

Only trends. The 6-minute walk distance tended to be maintained in the ACE-031 groups while it declined on placebo. There were also trends towards more lean mass and bone density and less fat mass. None of this was statistically significant.2

Is ACE-031 approved?

No. ChEMBL lists ramatercept with phase 2 as the highest phase. ClinicalTrials.gov lists four trials from 2008 to 2011, both phase 2 trials were terminated early (as of 26 October 2026).54

What do animal studies show?

In marmosets lean mass increased over 14 weeks on ACE-031, muscle fibres became thicker and muscle force rose. This did not happen in the control group. The authors see this as a pointer for muscle diseases in humans.3

Glossary

Terms explained briefly

Dotted words in the text open these explanations directly.

Activin receptor IIB
Receptor on muscle and other cells through which myostatin and activins send their braking signal.
Activins
Messengers from the same family as myostatin. Among other things they control growth and hormones.
Duchenne muscular dystrophy
Inherited muscle disease in boys in which the muscles get progressively weaker.
Fusion protein
Artificially joined protein made of two parts, here receptor plus antibody piece. This extends the duration of action.
Lean mass
Body weight without fat, mainly muscle, organs and bone.
Lyophilisate
Freeze-dried powder. Without water a compound keeps much longer.
Myostatin
The body's own messenger (GDF-8) that brakes muscle growth. Without it muscles grow more.
Subcutaneous
Into the fat layer just under the skin. This is how ACE-031 was given in the studies.
Telangiectasias
Permanently widened small blood vessels, visible as fine red lines.

Evidence

Sources

Show all 5 sourcesHide sources 3 Studies1 Trial registry1 Database checked 26 Oct 2026

Studies

  1. Single-dose study in healthy women (phase 1)

    Attie et al., Muscle & Nerve, 2013

    DOI 10.1002/mus.23539 PMID 23169607
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  2. Trial in boys with Duchenne muscular dystrophy, stopped early

    Campbell et al., Muscle & Nerve, 2017

    DOI 10.1002/mus.25268 PMID 27462804
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed
  3. Muscle mass and strength in marmosets

    Cadena et al., PLOS One, 2026

    DOI 10.1371/journal.pone.0342666 PMID 41686840
    Checked 26 Oct 2026 via doi.org, Crossref, PubMed

Trial registry

  1. Trials on ACE-031 on ClinicalTrials.gov

    ClinicalTrials.gov, U.S. National Library of Medicine

    Checked 26 Oct 2026 via ClinicalTrials.gov API v2

Database

  1. Ramatercept in ChEMBL (mechanism, phase)

    ChEMBL, EMBL-EBI (CHEMBL2108674)

    Checked 26 Oct 2026 via ChEMBL

In the shop

ACE-031 in the catalog

Sizes, prices and shipping times are on the product page.

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