ACE-031
Also called ACE031, activin receptor IIB fusion
ACE-031 is a decoy receptor for myostatin - the protein your body uses to put a ceiling on muscle growth.
Tested in smaller controlled human trials — real human data, at an early stage.
- Body composition
The quick answer
ACE-031 is a decoy receptor for myostatin - the protein your body uses to put a ceiling on muscle growth. Soak up myostatin and the ceiling lifts. It is one of very few things in this space that reached a real Phase 2 trial in people, and one of very few whose trial was stopped.
What it is not
Not a research chemical that simply never got tested. It was tested, in people, and stopped.
Why people use it
💪 A real and large muscle effect in the human trial - lean mass rose measurably; 🔬 Genuinely tested in people, unlike most of this category
What people report using
A human trial was halted for safety, so we will not put a number next to it. That is a deliberate choice, not a gap in the record.
What to expect, and when
The trial saw measurable lean mass change within weeks. The bleeding effects appeared on a similar timescale.
Side effects, and what people do about them
The trial in boys with Duchenne muscular dystrophy was stopped early after nosebleeds, gum bleeding and dilated surface blood vessels appeared. Those effects were not fatal and were attributed to how widely the target is used in the body, but they were enough to end the programme.
Go deeper
Open these only if you want them.
How it actually works
A soluble form of the activin type IIB receptor fused to an antibody fragment. It binds myostatin and related activins before they can reach the real receptor. Because ActRIIB also carries signals involved in blood-vessel regulation, blocking it broadly has effects well beyond muscle - which is exactly what the trial found.
More on the evidence
A phase 2 human trial was stopped early for safety — participants developed nosebleeds and dilated surface blood vessels (telangiectasia), which is a vascular signal rather than a nuisance side effect. Because development was halted rather than completed, no dose was ever established as usable and we publish no ladder for it. That is not caution on our part: there is genuinely nothing to publish. A compound whose trial was stopped for safety is a different category from one that was never tested at all, and it is the single most useful fact about this one.
What people report, in full
ACE-031 is unusual here in that the community discusses it in the past tense. It is the myostatin story that nearly worked - real lean mass gains in an actual human trial, then a halt for bleeding and visible blood-vessel changes. Very few people report having used it, and most of the discussion that exists is people explaining to each other why they did not. In a space where enthusiasm is the default, that is a meaningful signal. The related conversation worth knowing is about myostatin inhibition in general: community sentiment drifted from excitement to caution, largely because of what happened here.
Worth knowing
That is different from a trial that simply failed, and it is the thing to weigh hardest before deciding anything about this one.
The clearest case in this catalogue of tested and stopped. It worked on muscle. It was halted anyway. Both halves are true and both belong in the same breath.
Sources and review
This record is built on what the wider community reports doing and experiencing, summarised above. No counted dataset has been attached to this compound yet — when one is published, it goes here with its numbers.
Campbell C, 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. PMID 27462804.The phase 2 programme was stopped early over safety findings.
These references were located by literature search and recorded as the primary sources behind this record. The publishers block automated retrieval, so they are pointers to the right papers rather than quotations we have checked line by line. They are replaced as we read them properly.
Last reviewed 2026-09-08.
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Still not sure?
Ask it the way you would ask a person. Follow-up questions are the point — it remembers what you already said.
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