ACE-031 is not a small peptide fragment like most compounds on this site — it is a decoy receptor, an engineered protein built to intercept a natural "muscle brake" before it can act. It has genuinely rare human trial data for this category, including a measurable strength/mass signal — and an equally well-documented, specific reason its development stalled.
In plain terms: your body has a brake pedal for muscle growth. ACE-031 is a fake pedal sensor that soaks up the brake signal so it never reaches the real one.
What it is
Skeletal muscle growth is held in check by myostatin and related proteins (including activin A), which act through a cell-surface receptor called activin receptor type IIB (ActRIIB). ACE-031 is a fusion protein: the outward-facing (extracellular) part of the ActRIIB receptor — the piece that normally catches myostatin — fused to a fragment of human antibody (IgG1-Fc) so the whole construct circulates in the blood3.
How it is thought to work
Because ACE-031 carries the receptor's own "catcher's mitt," it competes with your real ActRIIB receptors for the same ligands. Myostatin and activin A bind to the circulating decoy instead of the receptor on muscle cells, so their brake signal never gets through3. With less of that brake pressed, muscle has more room to grow — the same broad strategy (blocking myostatin/activin signalling) used by other experimental muscle-growth approaches such as follistatin and bimagrumab, just via a different piece of the pathway.
In plain terms: it doesn't push the accelerator: it removes a foot from the brake.
What the studies actually found
ACE-031's evidence is unusual for this category — it includes two real human trials, not just animal work.
| Study | Model | Key result | Year |
|---|---|---|---|
| Attie et al. — phase 11 | 48 healthy postmenopausal women (single dose) | At the top dose (3 mg/kg), significant gains in total lean body mass (+3.3%) and thigh muscle volume (+5.1%) by day 29; generally well tolerated | 2013 |
| Campbell et al. — RCT2 | ambulatory boys with Duchenne muscular dystrophy | Trends toward preserved 6-minute-walk distance, more lean mass, and higher bone density versus placebo (not statistically significant) — but the study was stopped early for a specific safety signal | 2017 |
| Cadena et al. — preclinical (NHP)3 | common marmoset monkeys, 14 weeks | Confirmed increased muscle mass and strength in a non-human primate model | 2026 |
The phase-1 result is a genuine, published human signal of efficacy1 — something most compounds on this site don't have. But the more important result, for anyone weighing this compound honestly, is what happened next.
Why it stopped — the specific reason, not a vague one
The Duchenne muscular dystrophy trial was stopped after the second dosing regimen. The published report is explicit about why: not a muscle-related safety issue, and not a "serious or severe adverse event" in the strict sense — but epistaxis (nosebleeds) and telangiectasias (small abnormal blood-vessel growths) that were concerning enough on their own to end the study2. The authors note the trend toward benefit (walk distance, lean mass, bone density) did not reach statistical significance — partly because the trial was cut short before it could2.
This is a genuinely useful example of an honest drug-development story: real efficacy signal, stopped by an off-target safety finding, not by the mechanism failing.
The honest gaps
- No trials since 2017. There is no published human research on ACE-031 after the Duchenne study report. Its clinical development has not visibly continued.
- The vascular signal is unexplained here. The papers report *that* epistaxis and telangiectasias occurred, not a settled explanation of the underlying vascular mechanism — treat it as an observed, trial-ending finding, not a fully understood one.
- No approved use. ACE-031 has never been approved as a medicine for Duchenne muscular dystrophy or anything else.
Regulatory status
ACE-031 is not an approved medicine. Its most advanced human trial was stopped for safety reasons before efficacy could be confirmed statistically, and no further human trials have been published. This page explains what it is and what the studies showed — not how to use it — and it takes no position on sourcing.
The short version
ACE-031 is a soluble ActRIIB decoy receptor that soaks up myostatin and related muscle-limiting signals. Unusually for this category, it has real human data: a phase-1 trial showed measurable lean-mass and muscle-volume gains, but a follow-up Duchenne muscular dystrophy trial was stopped early for a specific, documented reason — nosebleeds and small vascular growths, not a muscle problem. It never reached approval and has no published trials since 2017. For other myostatin/activin-pathway peptides, see follistatin and bimagrumab. Educational overview only, not medical advice.