What Is ACE-031? Dosage, Half-Life & How to Track It

What ACE-031 is and how it works

ACE-031, generic name Ramatercept, is a lab-engineered fusion protein: the outer, ligand-binding piece of the activin receptor type IIB (ActRIIB) stitched to a human antibody fragment (IgG1 Fc). That Fc tail is what gives it a circulating half-life measured in days rather than minutes — a structural trick borrowed from antibody drugs, and the reason it behaves nothing like a small injectable peptide despite being grouped with them online.

It works as a decoy: it floats in the blood and intercepts myostatin — the body’s own brake on muscle growth — along with GDF-11, activins A and B, and two vascular-signaling proteins, BMP9 and BMP10, before any of them can reach the real receptor on muscle cells. That broad net is exactly what made it effective, and exactly what ended the program: BMP9/10 are essential for healthy blood-vessel walls, and blocking them produced the vascular side effects that halted development.

Phase 1 data was genuinely striking — a single injection produced measurable lean-mass and thigh-volume gains in healthy adults within two weeks. That result is why ACE-031 has a real underground following more than a decade after its official program ended, despite no approved version ever reaching market.

Dosing: clinical trial data vs. what is actually sold

Clinical trials dosed ACE-031 by body weight — up to 3 mg/kg in Phase 1, given subcutaneously every 2–4 weeks in Phase 2. That is a completely different scale from what circulates in the gray market, where flat 1 mg vials, dosed weekly or twice weekly, are the norm — a dose driven by vial economics, not by the trial data. For a 100 kg adult to hit the Phase 1 top dose would take 300 mg per injection; at gray-market pricing that is a five-figure cost, which is the practical reason nobody is actually replicating the clinical protocol.

Because gray-market vials sit one to two orders of magnitude below the clinical dose per kilogram, this table describes what people are actually injecting — not a validated therapeutic dose. The calculator handles the arithmetic either way.

The authenticity problem: what is actually in the vial

This is the single most important practical fact about ACE-031, and it is backed by peer-reviewed lab analysis, not forum rumor. A 2025 study tested 14 black-market products labeled ACE-031 using mass spectrometry: 2 of 14 contained no ACE-031-related protein at all (one was follistatin instead), and the remaining 12 contained full-length ACVR2B receptor protein — a structurally different molecule from the truncated, Fc-fused construct that defines real ACE-031.

The reason is manufacturing, not fraud alone: authentic ACE-031 requires mammalian cell culture to correctly glycosylate the protein, a level of bioprocessing far beyond what typical research-peptide labs run. Standard third-party purity testing used to verify small peptides cannot tell the difference between real ACE-031 and full-length ACVR2B. In plain terms: it is more likely than not that a vial bought online is not the compound the clinical trial data describes.

What to track & side effects

The vascular side effects that halted the Phase 2 trial — nosebleeds, gum bleeding, and visible dilated skin capillaries — showed up in a small treated cohort and were traced directly to BMP9/10 blockade, not to a dosing mistake; the trial was too small to put a reliable frequency on how often they occurred. That means the risk is built into the mechanism, not something a lower dose reliably avoids. ACE-031 is also explicitly named on the WADA prohibited list.

Anyone with a personal or family history of bleeding disorders, or currently on anticoagulants, has a materially higher-risk profile here than with most research peptides. What is worth tracking, beyond dose and timing, is exactly the kind of symptom that would otherwise get dismissed — unexplained nosebleeds or unusual bruising — logged the day it happens rather than recalled weeks later.

Frequently asked questions