--- canonical_name: ACE-031 alternate_names: Ramatercept, ACVR2B-Fc, ActRIIB-Fc, ActRIIB-IgG1 canonical_topic: ACE-031 for Muscle Growth short_topic_lc: ace_031_muscle creation_date: 2026-0913-1436 creator_ai_fullname: Opus 5 ep_keywords: Myostatin Inhibitors, Activin Receptor Type IIB Antagonists --- # ACE-031 for Muscle Growth
Evidence Review created on 09/13/2026 using [AI4L](https://github.com/forever-healthy/AI4L) / Opus 5 **Also known as:** Ramatercept, ACVR2B-Fc, ActRIIB-Fc, ActRIIB-IgG1 ## Motivation ACE-031 (ramatercept) is a laboratory-made protein designed to make skeletal muscle larger. It acts as a decoy: released into the bloodstream, it soaks up myostatin and several closely related signals that the body uses to limit how much muscle it builds. Remove those signals and muscle fibers enlarge. That simple idea made the compound one of the first serious attempts to grow human muscle by chemistry rather than by training alone. The compound was created roughly fifteen years ago by a biotechnology company aiming at muscle-wasting disease, not at athletic performance. It was tested in healthy volunteers and in boys with a severe inherited muscle disorder, and the program was stopped early after unexpected effects on small blood vessels appeared. Development was never resumed. Since then the compound has resurfaced on the grey market and is prohibited in competitive sport. This review examines what the human and animal evidence actually shows about ACE-031 and muscle growth: how much muscle it added, whether that muscle did more work, what harms appeared and why, and how much of the record rests on the company that owned the compound. **[Benefits](#expected-benefits) - [Risks](#potential-risks--side-effects) - [Protocol](#therapeutic-protocol) - [Conclusion](#conclusion)** ## Recommended Reading High-level expert commentary and narrative sources that frame ACE-031 and the wider practice of blocking muscle-growth inhibitors. * [#291 ‒ The role of testosterone in males and females, performance-enhancing drugs, sustainable fat loss, supplements, and more – Derek, More Plates More Dates Pt.2](https://peterattiamd.com/derekmpmd2/) - Peter Attia A dedicated segment weighs the online enthusiasm for growing muscle by blocking myostatin against what human and animal data actually support — the therapeutic category ACE-031 belongs to. * [Myostatin/Activin Receptor Ligands in Muscle and the Development Status of Attenuating Drugs](https://pubmed.ncbi.nlm.nih.gov/34520530/) - Rodgers & Ward, 2022 The most complete narrative map of every drug built to block this pathway, including why several programs failed on treatment-related adverse events rather than on lack of muscle growth. * [Challenges and Future Prospects of Targeting Myostatin/Activin A Signaling to Treat Diseases of Muscle Loss and Metabolic Dysfunction](https://pubmed.ncbi.nlm.nih.gov/36738276/) - Lee et al., 2023 A candid review by the discoverer of myostatin and industry co-authors on why twenty-five years of trials produced muscle mass but rarely muscle function. * [Gel Electrophoretic Detection of Black Market ACE-031](https://pubmed.ncbi.nlm.nih.gov/40312924/) - Reichel et al., 2025 Laboratory analysis of fourteen grey-market ACE-031 products, the only direct evidence on what people buying this compound today actually receive. * [ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (*Callithrix jacchus*)](https://pubmed.ncbi.nlm.nih.gov/41686840/) - Cadena et al., 2026 The long-delayed primate study of ACE-031 itself, reporting fiber-level growth and contractile force measurements that human trials never obtained. **Note on priority sources:** Only Peter Attia's platform carried substantive discussion of this therapeutic category. FoundMyFitness returned brief news items that mention myostatin in vitamin D and transgenic-animal contexts, and Life Extension's Catabolic Wasting protocol names ACE-031 in a single paragraph reporting the Phase 1 thigh-muscle result; Huberman Lab, Chris Kresser and Lifespan.io returned nothing on myostatin inhibition or ACE-031. None of these treats the topic in the depth this section requires, so none was listed. ## Grokipedia No Grokipedia article exists for ACE-031. ## Examine No Examine article exists for ACE-031. ACE-031 is an unapproved injectable biologic rather than a dietary supplement, and Examine.com does not typically cover prescription or investigational medications. ## ConsumerLab No ConsumerLab article exists for ACE-031. ACE-031 is an unapproved injectable biologic rather than a dietary supplement, and ConsumerLab does not typically cover prescription or investigational medications. ## Systematic Reviews No systematic review or meta-analysis examines ACE-031 itself, so the papers below pool trials of other agents that block the same receptor or the same ligands, and each annotation names the agent actually tested. * [Efficacy and Safety of Bimagrumab in Adults With Obesity and Metabolic Dysfunction: A Systematic Review and Meta-Analysis of Randomized Controlled Trials](https://pubmed.ncbi.nlm.nih.gov/42530342/) - Shao et al., 2026 Pools four randomized trials of bimagrumab, not ACE-031, quantifying both lean-mass gain and the harms of blocking this receptor. * [Blocking the activin IIB receptor with bimagrumab (BYM338) increases walking performance: A meta-analysis](https://pubmed.ncbi.nlm.nih.gov/34405505/) - Spitz et al., 2021 Pools four bimagrumab trials, not ACE-031, on the six-minute walk test — the closest the class comes to a pooled functional outcome. * [Effect of Bimagrumab on body composition: a systematic review and meta-analysis](https://pubmed.ncbi.nlm.nih.gov/39251484/) - Kanbay et al., 2024 Pools seven randomized trials of bimagrumab, not ACE-031, finding gains in muscle volume and fat-free mass without matching strength or physical performance. * [Myostatin Modulation in Spinal Muscular Atrophy: A Systematic Review of Preclinical and Clinical Evidence](https://pubmed.ncbi.nlm.nih.gov/40565321/) - Gnazzo et al., 2025 Reviews myostatin-pathway agents in spinal muscular atrophy, chiefly apitegromab rather than ACE-031, and finds target engagement without robust large-trial efficacy. * [Efficacy and safety of pharmacological treatments in inclusion body myositis: a systematic review](https://pubmed.ncbi.nlm.nih.gov/39843353/) - Santos et al., 2025 Includes bimagrumab, not ACE-031, among drugs judged to have no effect on disease progression despite measurable muscle enlargement. The claimed effect (muscle enlargement) and the principal risks (adverse events, discontinuation) are both represented, the first two papers covering each. No systematic review or meta-analysis addresses the vascular harms that specifically halted ACE-031; that evidence exists only at the level of single trials. ## Mechanism of Action ACE-031 is a soluble decoy receptor: the ligand-binding portion of the activin receptor type IIB (ActRIIB, the muscle-cell docking point for growth-limiting proteins) fused to the Fc fragment (an antibody's tail, which extends a protein's life in blood) of human immunoglobulin G1 (IgG1, the commonest antibody class). Circulating freely, it captures myostatin (GDF-8, growth differentiation factor 8), activin A, activin B and GDF-11 before they reach the muscle cell. Those ligands normally dock on ActRIIB, which recruits a partner receptor (ALK4 or ALK5, activin receptor-like kinases) and switches on Smad2 and Smad3, messenger proteins carrying the signal to the nucleus. There it damps the Akt–mTOR pathway (mechanistic target of rapamycin, the cell's master switch for assembling protein) and speeds protein breakdown. Removing the ligands releases that brake, enlarging both slow and fast fibers ([Cadena et al., 2010](https://pubmed.ncbi.nlm.nih.gov/20466801/), run by Acceleron Pharma, the compound's owner). Two readings compete: that broad capture is what makes the approach work, because activin A rather than myostatin drives most of the gain; or that the same breadth removes BMP9 and BMP10 (bone morphogenetic proteins that stabilize small blood vessels) and causes the vascular toxicity ([Rodgers & Ward, 2022](https://pubmed.ncbi.nlm.nih.gov/34520530/)). Given subcutaneously, ACE-031 shows dose-proportional exposure from 0.02 to 3 mg/kg and a half-life of 10–15 days. It stays in plasma and interstitial fluid, does not enter the brain, and is cleared by protein catabolism with FcRn (neonatal Fc receptor) recycling rather than by liver enzymes such as CYP3A4 (a major drug-metabolizing enzyme) ([Attie et al., 2013](https://pubmed.ncbi.nlm.nih.gov/23169607/)). ## Historical Context & Evolution ACE-031 was built for disease, not for performance. It emerged from Acceleron Pharma, a Cambridge biotechnology company that also developed the closely related receptor traps sotatercept and luspatercept, and its stated target was Duchenne muscular dystrophy (DMD, an inherited disorder in which muscle progressively degenerates). The scientific opening came from [the 1997 discovery](https://pubmed.ncbi.nlm.nih.gov/9139826/) that animals lacking myostatin carry roughly double the muscle of normal littermates, a finding later matched in cattle breeds and in a child with an inactivating mutation. The clinical record is short. A single-ascending-dose study in 48 healthy postmenopausal women found dose-linear exposure and measurable muscle enlargement ([Attie et al., 2013](https://pubmed.ncbi.nlm.nih.gov/23169607/)). A multiple-dose study in 70 healthy postmenopausal women followed ([NCT00952887](https://clinicaltrials.gov/study/NCT00952887)), and a Phase 2 trial randomized 24 ambulatory boys with DMD ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761)). The Phase 2 trial and its extension were halted in 2011. The published report attributes the decision to nosebleeds and telangiectasias (clusters of widened small blood vessels) observed in the boys, alongside a trend toward preserved walking distance and increased lean mass and bone density ([Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)); the sponsor's registry entry additionally cites concerns about long-term adverse reactions identified in chronic animal toxicity work. Opinion moved, but it did not close. The reading that ACE-031 was too indiscriminate motivated a generation of narrower agents — receptor antibodies, anti-myostatin antibodies and pro-myostatin binders — and their trials have since produced their own disappointments on function, so the question of whether breadth or selectivity is correct remains genuinely open ([Lee et al., 2023](https://pubmed.ncbi.nlm.nih.gov/36738276/)). ## Expected Benefits Almost all of the evidence below was generated, analyzed and reported by Acceleron Pharma, the company that owned ACE-031: the Phase 1 report is authored entirely by Acceleron staff, the rodent and marmoset studies were run by Acceleron scientists, and the Phase 2 trial was sponsored by Acceleron with company employees among its authors. This is a direct financial interest in the compound's adoption and it applies to every effect estimate in this section. ### High 🟩 🟩 🟩 #### Increase in Skeletal Muscle Mass ACE-031 enlarges existing muscle fibers by removing the growth-limiting signals that normally restrain them. The effect appears in both published human trials: whole-body lean mass and thigh muscle volume rose after a single dose in healthy postmenopausal women, and lean mass rose again over twelve weeks of repeat dosing in boys with Duchenne muscular dystrophy. Gains were measured by imaging, not by strength testing, and the same Duchenne trial found no corresponding gain in muscle force. Only the single-dose trial reached statistical significance against placebo. **Magnitude:** +3.3% total body lean mass and +5.1% thigh muscle volume at day 29 after a single 3 mg/kg dose versus placebo ([Attie et al., 2013](https://pubmed.ncbi.nlm.nih.gov/23169607/)); +4.1% (1.0 mg/kg every 2 weeks) and +3.6% (0.5 mg/kg every 4 weeks) versus +2.6% on placebo over 24 weeks in Duchenne boys — each drug arm's own change from baseline reached p = 0.012 and p = 0.023 respectively (p, the probability that a difference this large would arise by chance alone) against p = 0.435 on placebo, while the published report describes the drug-versus-placebo difference as a non-significant trend ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761); [Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)). ### Medium 🟩 🟩 #### Increase in Bone Mineral Density ⭕️ Not Central to Muscle Growth Blocking this receptor also removes a brake on bone formation, so lumbar spine bone mineral density (BMD, the standard measure of skeletal strength) rose in the Duchenne trial and bone-formation markers shifted favorably in the Phase 1 study. This bears on fracture risk and skeletal resilience rather than on muscle growth. Evidence rests on one controlled trial with BMD as an endpoint, in a population with corticosteroid-related bone loss, so the size of any effect in healthy adults is unknown. **Magnitude:** lumbar spine BMD +4.4% (1.0 mg/kg every 2 weeks) and +1.6% (0.5 mg/kg every 4 weeks) versus +0.3% on placebo over 24 weeks; the higher-dose arm's own change from baseline reached p = 0.039, while the published report describes the bone effect as a trend ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761); [Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)). ### Low 🟩 #### Reduction in Fat Mass ⭕️ Not Central to Muscle Growth Fat mass fell in both ACE-031 arms of the Duchenne trial while rising on placebo, and Phase 1 serum markers pointed the same way. This bears on body composition, not on muscle growth. Rodent work is inconsistent, with [one diet-induced obesity model](https://pubmed.ncbi.nlm.nih.gov/22023380/) showing no fat loss at all. **Magnitude:** fat mass fell in both ACE-031 arms of the Duchenne trial and rose on placebo, an effect reported only as a directional trend; the publication gives no effect-size figure for this endpoint ([Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)). #### Maintenance of Walking Distance ⚠️ Conflicted Six-minute walk distance was the Duchenne trial's functional endpoint, reported by age stratum. Under ten, the lower-dose arm gained and the higher-dose arm did not; at ten and over, both drug arms held steady while placebo fell. Net reading: the direction reverses between strata, so walking benefit is unproven. **Magnitude:** under 10 years at baseline, +43.8 m (0.5 mg/kg every 4 weeks) and +2.5 m (1.0 mg/kg every 2 weeks) versus +5.2 m on placebo; at 10 years and over, +4.5 m and −3.2 m versus −47.6 m on placebo; over 24 weeks, no comparison statistically significant ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761); [Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)). ### Speculative 🟨 #### Protection Against Disuse and Diet-Induced Muscle Loss No controlled human study has tested ACE-031 against immobilization, bed rest or energy restriction. The basis is mechanistic plus animal: the same receptor blockade preserved muscle in rodent and primate models ([Cadena et al., 2026](https://pubmed.ncbi.nlm.nih.gov/41686840/)). #### Increase in Muscle Force Human strength testing in the Duchenne trial was flat. The only force data come from isolated marmoset muscle after fourteen weeks — an animal measurement, not a human outcome ([Cadena et al., 2026](https://pubmed.ncbi.nlm.nih.gov/41686840/)). ## Benefit-Modifying Factors * **Myostatin-pathway genotype (MSTN, ACVR2B):** MSTN encodes myostatin itself and ACVR2B encodes the receptor ACE-031 mimics. Carriers of inactivating variants already run with the brake partly released, leaving less headroom for a further increase in muscle mass. * **Baseline activin A and myostatin levels:** Circulating levels of these growth-limiting proteins rise with aging, obesity and chronic illness. A higher starting level means more ligand available to trap, and plausibly a larger response than in a young, lean, already-trained person. * **Baseline lean mass and training status:** Trial gains of 3–5% were measured against untrained or disease-affected baselines. Someone already near their trained ceiling has proportionally less untapped fiber cross-sectional area, so the same dose should yield a smaller relative increase. * **Sex:** Every published human dataset is either postmenopausal women or prepubertal boys. No adult man has been dosed in a published trial, so the interaction between ACE-031 and an adult male androgen environment is entirely uncharacterized. * **Pre-existing conditions:** Muscle-wasting states driven by activin A, such as cachexia (severe illness-related muscle and weight loss) and corticosteroid-treated dystrophy, offer the largest theoretical benefit, while conditions that limit protein intake or mobility cap what added fiber size can deliver. * **Age:** Older adults carry higher activin A and more room for lean-mass gain, but the trials enrolled only boys and postmenopausal women. At the older end of the adult range, benefit is plausible while the bleeding risks below also rise. ## Potential Risks & Side Effects As in the benefits section, every human safety observation below comes from trials sponsored, conducted and reported by Acceleron Pharma, the compound's owner — a party with a direct financial interest in the compound's fate. ### High 🟥 🟥 🟥 #### Injection-Site Reactions Redness at the injection site was the most common adverse event in the Phase 1 study and recurred in the Phase 2 trial, making it the only harm documented in more than one trial. It reflects local immune response to a large foreign protein delivered subcutaneously. It was self-limiting and no participant discontinued for it. Notably, the placebo arm of the Duchenne trial reported a similar rate, so part of this is the injection rather than the drug. **Magnitude:** injection-site erythema in 6/9 (67%) on 1.0 mg/kg every 2 weeks and 3/9 (33%) on 0.5 mg/kg every 4 weeks versus 3/6 (50%) on placebo in the Duchenne trial ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761)); the leading adverse event in the single-dose study ([Attie et al., 2013](https://pubmed.ncbi.nlm.nih.gov/23169607/)). ### Medium 🟥 🟥 #### Telangiectasias and Nosebleeds This is the harm that ended the program. Telangiectasias (clusters of permanently widened small blood vessels visible in the skin or mucous membranes) and epistaxis (nosebleeds) appeared together and dose-dependently in the Duchenne trial. The accepted mechanism is that a broad receptor trap also captures BMP9 and BMP10, the ligands whose signaling keeps small vessels stable; inherited loss of that same signaling causes hereditary hemorrhagic telangiectasia ([Tillet & Bailly, 2014](https://pubmed.ncbi.nlm.nih.gov/25620979/)). Evidence rests on one controlled trial. **Magnitude:** epistaxis in 5/9 (56%) and telangiectasia in 5/9 (56%) on 1.0 mg/kg every 2 weeks, versus 1/9 and 0/9 on 0.5 mg/kg every 4 weeks and 0/6 for both on placebo ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761); [Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)). #### Headache Headache occurred more often on ACE-031 than on placebo in the Duchenne trial ([Campbell et al., 2017](https://pubmed.ncbi.nlm.nih.gov/27462804/)) and was not severe. Whether it is a separate effect or an early marker of the same small-vessel changes that produced the telangiectasias is unresolved, since no imaging or vascular assessment accompanied it. Evidence rests on one controlled trial with very small arms. **Magnitude:** headache in 3/9 (33%) on 1.0 mg/kg every 2 weeks and 1/9 (11%) on 0.5 mg/kg every 4 weeks versus 1/6 (17%) on placebo ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761)). ### Low 🟥 #### Adulterated and Misidentified Grey-Market Product No licensed supply exists, so ACE-031 is bought as an unregulated research chemical, and laboratory analysis shows the labels are wrong. Most tested vials held full-length activin receptor IIB rather than the fusion protein, plus many other proteins. What is actually injected, and its sterility, is unknown. **Magnitude:** 12/14 (86%) of tested products contained a different protein than labeled and 2/14 (14%) contained none; none contained genuine ACE-031 ([Reichel et al., 2025](https://pubmed.ncbi.nlm.nih.gov/40312924/)). ### Speculative 🟨 #### Increase in Red Cell Mass No hemoglobin or hematocrit data have been published for ACE-031 in humans. The concern is mechanistic and class-based: related activin receptor traps reliably raise red blood cells and hemoglobin ([Carrancio et al., 2014](https://pubmed.ncbi.nlm.nih.gov/24635723/)). #### Testicular Changes and Impaired Fertility Long-term blockade of activin and myostatin signaling produced persistent testicular abnormalities in mice, an effect that outlasted treatment ([Vaughan et al., 2021](https://pubmed.ncbi.nlm.nih.gov/33408083/)). No human gonadal data exist for ACE-031; the basis is animal work alone. #### Vascular Malformations Beyond Skin and Mucosa If the vascular effect is BMP9/BMP10 loss, the inherited disease modeling it produces arteriovenous malformations (abnormal artery-to-vein connections) in lung, liver and brain. None appeared in the short human trials; the basis is mechanistic analogy. ## Risk-Modifying Factors * **Vascular genotype (ENG, ACVRL1, SMAD4):** These genes encode the receptor and signaling partners for BMP9 and BMP10. Carriers of loss-of-function variants already have destabilized small vessels, so pharmacological removal of the same ligands would compound an existing defect. * **Baseline hematology:** A starting hemoglobin or hematocrit near the upper limit leaves no margin for the red-cell rise seen with related receptor traps, and a low platelet count removes what limits small-vessel fragility becoming visible bleeding. * **Sex:** All human safety data come from postmenopausal women and prepubertal boys. Men carry higher baseline hematocrit, which plausibly narrows the margin before red-cell excess, and only males were affected in the rodent gonadal findings. * **Pre-existing conditions:** Bleeding disorders, peptic ulcer disease, hereditary hemorrhagic telangiectasia, known arteriovenous malformations, uncontrolled hypertension and polycythemia (an excess of red blood cells) all sit directly downstream of the compound's documented vascular effect. * **Age:** Older adults have more fragile mucosal vessels, higher rates of anticoagulant and antiplatelet use, and a higher background incidence of vascular malformations, so the same dose-dependent bleeding signal seen in boys would be expected to carry heavier consequences. ## Key Interactions & Contraindications * **Oral anticoagulants (warfarin, apixaban, rivaroxaban, dabigatran):** Caution bordering on absolute contraindication. ACE-031's small-vessel fragility plus impaired clotting raises the risk of prolonged epistaxis and gastrointestinal bleeding. No dose adjustment mitigates this; the combination is best avoided entirely. * **Antiplatelet drugs (aspirin, clopidogrel, ticagrelor, prasugrel):** Caution. Additive bleeding risk through a second, independent mechanism. Where antiplatelet therapy is medically required, it takes precedence and ACE-031 is the agent to omit. * **Over-the-counter analgesics (aspirin, ibuprofen, naproxen, diclofenac gel):** Caution. Non-steroidal anti-inflammatory drugs (NSAIDs, pain relievers that also inhibit platelets and irritate gastric mucosa) add both bleeding tendency and mucosal injury. Substituting paracetamol removes the interaction. * **Erythropoiesis-stimulating agents (epoetin alfa, darbepoetin alfa):** Caution. Both raise red cell mass; combined use risks hyperviscosity (blood thickening) and thrombosis. The ACE-031 Phase 1 protocol excluded anyone treated with these agents within two months, and that separation is the practical mitigation. * **Other activin-pathway agents (bimagrumab, apitegromab, luspatercept, sotatercept, taldefgrobep alfa, follistatin gene therapy):** Absolute contraindication to combining. These act on the same ligands or receptor; stacking multiplies vascular and erythroid effects without adding muscle. Only one such agent at a time. * **Supplements with additive bleeding effects:** Caution. High-dose fish oil (the omega-3 fats EPA and DHA), vitamin E above 400 IU, *Ginkgo biloba*, concentrated garlic extract, nattokinase and high-dose curcumin all inhibit platelets. Stopping them, or separating use, reduces additive mucosal bleeding. * **Supplements with additive effects on muscle mass:** Monitor only. Creatine monohydrate, HMB (beta-hydroxy beta-methylbutyrate, a leucine metabolite) and epicatechin-containing extracts marketed as myostatin blockers add to lean mass and to water retention, confounding any assessment of what ACE-031 itself is doing. * **GLP-1 receptor agonists (semaglutide, tirzepatide, liraglutide):** Monitor. GLP-1 (glucagon-like peptide-1) agonists cause weight loss that includes lean tissue; pairing is the explicit rationale of several current trials. Consequence is an altered body-composition trajectory, not toxicity. * **Anabolic androgenic steroids and selective androgen receptor modulators:** Caution. Both raise hematocrit independently, compounding the class-level red-cell rise, and both add cardiovascular strain. Hematocrit monitoring, or avoiding the combination, is the mitigation. **Populations who should avoid ACE-031:** * Anyone with hereditary hemorrhagic telangiectasia, or a first-degree relative with it * Anyone with a known pulmonary, hepatic or cerebral arteriovenous malformation * Anyone on therapeutic anticoagulation, or with an inherited bleeding disorder such as von Willebrand disease or hemophilia * Anyone with a gastrointestinal bleed or active peptic ulcer within the previous 6 months * Anyone with a platelet count below 100 × 10⁹/L * Anyone with polycythemia (hematocrit above 52% in men or above 48% in women) * Anyone with uncontrolled hypertension (above 160/100 mmHg) * Children and adolescents under 18 years, the population in which the program was halted * Anyone pregnant, attempting conception or breastfeeding * Anyone subject to anti-doping testing, for whom the compound is prohibited at all times ## Risk Mitigation Strategies * **Independent identity testing before any use:** Because 12 of 14 grey-market products contained the wrong protein, mass spectrometry or gel-based identity confirmation from an independent laboratory is the only defence against injecting an unidentified biologic. * **Lowest documented dose, longest documented interval:** Telangiectasias appeared in 5 of 9 boys on 1.0 mg/kg every 2 weeks and in 0 of 9 on 0.5 mg/kg every 4 weeks, making dose and frequency the primary levers on vascular harm. * **Baseline and periodic hematology:** Complete blood count before starting and every 8–12 weeks detects the red-cell rise seen with related receptor traps before hematocrit reaches the 52% threshold at which hyperviscosity and thrombosis risk climb. * **Structured skin and mucosal inspection:** Weekly self-inspection of lips, nail beds, fingers and nasal mucosa catches telangiectasias, the earliest visible marker of the small-vessel effect, while they are still few and before nosebleeds begin. * **Platelet-inhibiting agents withdrawn before starting:** Stopping aspirin, NSAIDs, high-dose fish oil, vitamin E, *Ginkgo biloba* and nattokinase at least 7 days before starting removes the additive contribution to mucosal bleeding from a second mechanism. * **Defined stopping rules:** Predefined discontinuation on any new telangiectasia, any nosebleed lasting over 10 minutes, or hematocrit above 52%, converts an open-ended exposure into a bounded one and prevents progression of the vascular effect. * **Short, bounded exposure with a washout:** Limiting any course to roughly 12 weeks followed by a 10-week washout mirrors the longest dosing period completed in humans and avoids the chronic exposure that produced animal toxicity. ## Therapeutic Protocol * **No approved or practitioner-established protocol exists:** ACE-031 was never approved anywhere and no clinic or physician prescribes it. Every regimen described below is a discontinued trial protocol designed by Acceleron Pharma, not a standard of care. * **Single-dose range studied:** 0.02 to 3 mg/kg by subcutaneous injection, dose-proportional in exposure. Muscle enlargement reached significance only at 3 mg/kg ([Attie et al., 2013](https://pubmed.ncbi.nlm.nih.gov/23169607/)). * **Repeat-dose regimens studied:** 0.5 mg/kg every 4 weeks or 1.0 mg/kg every 2 weeks, subcutaneously, for 12 weeks ([NCT01099761](https://clinicaltrials.gov/study/NCT01099761)). A planned 2.5 mg/kg every 4 weeks arm was never dosed because the trial stopped. * **Competing approach — progressive resistance training:** Resistance training with adequate protein produces lean-mass gains of comparable magnitude over the same twelve weeks, carries no vascular risk, and unlike ACE-031 has demonstrated strength gains alongside size. * **Competing approach — selective pathway agents:** Bimagrumab, apitegromab, trevogrumab and taldefgrobep alfa target the same axis more narrowly and remain in active trials. Neither approach is established; both have produced mass more readily than function. * **Best time of day:** Irrelevant. With a half-life of 10–15 days, plasma concentration is essentially flat across any 24-hour period, and no trial varied dosing time or reported a circadian effect. * **Half-life:** 10–15 days, measured across the full 0.02–3 mg/kg range. Steady state is approached after roughly 6–10 weeks of every-2-week dosing, which is why effects were assessed at 12 and 24 weeks. * **Single versus split dosing:** All trials used a single subcutaneous injection per administration. Splitting a dose has no pharmacological rationale given the long half-life and would only multiply injection-site reactions. * **Genetic polymorphisms influencing dose choice:** Variants in ENG, ACVRL1 and SMAD4 (the BMP9/BMP10 signaling genes) argue against any dose; MSTN and ACVR2B variants that already raise muscle mass argue for expecting less from a given dose. * **Sex-based differences:** No adult man has been dosed in a published trial. Dosing was weight-based in both sexes studied, and no sex-specific pharmacokinetic adjustment was ever established or tested. * **Age-related considerations:** Doses were weight-normalized in boys aged 4 and over and in women aged 45–75. No geriatric dose adjustment exists, and the higher background vascular fragility of older adults argues for the lower end of the studied range. * **Baseline biomarkers influencing response:** Higher baseline activin A and lower baseline lean mass predict a larger response in principle, but no trial stratified on either, so neither has been validated as a dosing input. * **Pre-existing conditions influencing response:** Corticosteroid-treated dystrophy and cachectic states carry the most ligand to trap and showed the clearest bone and lean-mass responses; healthy, well-trained physiology showed the smallest relative change. ## Discontinuation & Cycling * **Intended duration:** Trial exposure never exceeded 12 weeks of dosing. ACE-031 was designed as chronic therapy for progressive disease, but no human has been treated long enough to characterize either sustained benefit or cumulative harm. * **Stopping is abrupt by design:** Both Phase 2 trials were terminated outright, with participants followed for a further 12 weeks. No withdrawal syndrome, rebound weakness or adrenal-style dependence was reported on abrupt cessation. * **Withdrawal effects:** None described in humans. The expected consequence is loss of the added muscle, since the ligands resume signaling as drug clears, but no trial measured lean mass long enough after stopping to quantify the regression. * **Tapering:** Not applicable and not possible in any meaningful sense. A 10–15 day half-life means the compound self-tapers over roughly 6–10 weeks, and no receptor upregulation or rebound mechanism exists that tapering would address. * **Reversibility of the vascular effect:** Telangiectasias are structural lesions, not a pharmacological state. Whether those that appeared in the Duchenne trial fully resolved after stopping was never reported, which is an unresolved gap rather than reassurance. * **Cycling:** No efficacy rationale exists — the mechanism involves ligand sequestration rather than receptor downregulation, so tolerance is not expected. Any cycling is a safety measure to bound cumulative vascular exposure, not a way to maintain response. ## Sourcing and Quality * **No legitimate source exists:** ACE-031 has no marketing authorization in any jurisdiction, no licensed manufacturer and no pharmaceutical-grade supply. Every unit in circulation is an unregulated research chemical sold outside medical channels. * **Compounding pharmacies cannot supply it:** It is a recombinant fusion protein, not a compoundable small-molecule active ingredient, so no licensed compounding pharmacy in the United States or Europe can lawfully prepare it. Offers claiming otherwise are not legitimate. * **Documented composition failures:** Of 14 grey-market products analyzed, 12 contained full-length activin receptor IIB rather than the Fc-fusion protein, 2 contained no receptor protein at all, and all 12 carried numerous additional proteins ([Reichel et al., 2025](https://pubmed.ncbi.nlm.nih.gov/40312924/)). * **What independent testing must show:** Identity by mass spectrometry, not merely an immunoassay; confirmation that the Fc fragment is present, which protease cleavage testing detects; purity by gel separation; and endotoxin and sterility results, since the product is injected. * **Formulation and handling:** Genuine trial material was a lyophilized (freeze-dried) powder reconstituted with sterile water and stored refrigerated. Grey-market vials arrive without validated cold-chain records, so protein degradation and aggregation cannot be excluded. * **Third-party testing has hard limits here:** A certificate of analysis supplied by the vendor is not independent verification, and the published analysis shows vendor labelling to be unreliable in this specific compound. Only a buyer-commissioned independent laboratory result carries information. ## Practical Considerations * **Time to effect:** Measurable lean-mass and muscle-volume change appeared within 29 days of a single dose and was established by 12 weeks of repeat dosing. Visible or functional change on that timescale has never been demonstrated. * **Common pitfall — expecting strength:** The consistent finding across this entire drug class is that added muscle size does not reliably become added force. Both the Duchenne strength testing and [pooled trials of related agents](https://pubmed.ncbi.nlm.nih.gov/39251484/) show mass without proportional function. * **Common pitfall — dose escalation:** The vascular harm was dose-dependent while the lean-mass gain differed little between the two studied regimens, so raising the dose buys disproportionately more risk than benefit. * **Common pitfall — ignoring the vial's contents:** Most purchasers assume they are injecting ACE-031. The published analysis shows almost none of them are, which makes any personal dose-response reasoning unfounded. * **Regulatory status:** No approval anywhere, and no open FDA (U.S. Food and Drug Administration) pathway since development was abandoned. It is not a dietary supplement, and it is prohibited at all times under section S4.3 of the WADA (World Anti-Doping Agency) list. * **Note on the anti-doping evidence:** The detection studies cited here originate from WADA-accredited laboratories, whose funding follows from the prohibited-list mandate they administer. That interest does not bear on the compositional findings, which are instrumental measurements, but it is worth naming. * **Cost and accessibility:** Grey-market vials are cheap relative to approved biologics, and this asymmetry matters: insurers and health systems have a systematic incentive to favor exercise and nutrition over any costly muscle-targeting biologic, which shapes research funding and guidelines for age-related muscle loss. ## Interaction with Foundational Habits * **Sleep:** No direct interaction. ACE-031 has no central nervous system exposure and no trial reported sleep disturbance. The indirect consideration runs the other way: growth-hormone release during deep sleep drives the anabolic signaling that any added fiber cross-section depends on, so short sleep would blunt the benefit rather than the drug affecting sleep. * **Nutrition:** Potentiating and rate-limiting. Larger fibers require substrate, so protein intake in the region of 1.6–2.2 g/kg body weight daily and an energy intake at or above maintenance set the ceiling on what receptor blockade can deliver. Iron and folate status matter separately, given the class-level rise in red cell production. * **Exercise:** Potentiating in animals, untested in humans. Resistance training and ligand blockade act through partly separate routes — mechanical loading via the Akt–mTOR pathway, the drug via removal of Smad-mediated suppression — so effects should add rather than conflict. No published trial combined them, and no timing relative to injection has been studied. * **Stress management:** Indirect and antagonistic. Chronic cortisol elevation, whether from psychological stress or corticosteroid therapy, upregulates the very muscle-breakdown machinery ACE-031 suppresses; the Duchenne participants were all on corticosteroids, which plausibly dampened the observed response. ## Monitoring Protocol & Defining Success Before any exposure, the priority is establishing whether the two documented harm pathways — small-vessel fragility and rising red cell mass — have any pre-existing head start. That means a complete blood count with hematocrit and platelets, a metabolic panel covering liver and kidney function, blood pressure, iron studies, and a documented skin and mucosal examination photographed for later comparison. Body composition by DXA (dual-energy X-ray absorptiometry, a scan that separates lean mass, fat and bone) anchors the only endpoint the compound has actually been shown to move. Ongoing monitoring follows the trial cadence: bloods and blood pressure at 4 weeks, then every 8–12 weeks; skin and mucosal inspection weekly; DXA at 12 weeks and again at 24 weeks. Success means measurable lean-mass gain with hematocrit and vascular findings unchanged. | Biomarker | Optimal Functional Range | Why Measure It? | Context/Notes | |-----------|-------------------------|-----------------|---------------| | Hematocrit | 40–48% (men), 36–44% (women) | Detects the red-cell rise seen with related receptor traps | Conventional labs flag only above 52%/48%; hyperviscosity risk climbs well before that. Same-day hydration status shifts the value | | Hemoglobin | 13.5–16.0 g/dL (men), 12.0–14.5 g/dL (women) | Confirms an isolated hematocrit shift is real erythropoiesis | Conventional upper limits near 17.5 g/dL (men) and 15.5 g/dL (women) sit well above the functional ceiling. Pair with ferritin and reticulocyte count; a rise with falling ferritin indicates accelerated red-cell production | | Platelet count | 200–350 × 10⁹/L | Determines how far vessel fragility translates into bleeding | Conventional range extends to 150; below 150 offers no reserve against mucosal bleeding. Draw with the complete blood count | | Ferritin | 50–150 ng/mL | Tracks iron drawn down by increased red-cell production | Conventional ranges start near 15–30 ng/mL, far below the functional floor. Acute-phase reactant — interpret alongside hs-CRP (high-sensitivity C-reactive protein, an inflammation marker). Fasting preferred | | Blood pressure | Below 120/80 mmHg | Higher pressure amplifies fragile small-vessel bleeding | Measure seated after 5 minutes rest, both arms initially; morning readings are most reproducible | | Lean body mass (DXA) | No established target; track percentage change from the individual's own baseline, with trial gains of 3–5% over 12 weeks as the reference | The only outcome ACE-031 has been shown to move in humans | Same scanner, same hydration state, fasted; day-to-day fluid shifts of 1–2% otherwise dominate the signal | | Lumbar spine bone mineral density (DXA) | T-score above -1.0 | Captures the bone effect seen alongside muscle gain | Obtained from the same DXA appointment; meaningful change needs 12 months in most adults | | ALT | 10–26 U/L (men), 7–22 U/L (women) | Baseline organ safety and a check on concurrent substances | ALT is alanine aminotransferase, a liver enzyme. Conventional upper limits near 40–55 U/L are far above the functional range. Rises after heavy resistance training — allow 72 hours | | eGFR | Above 90 mL/min/1.73 m² | Baseline organ safety before an unlicensed injectable | eGFR is the estimated glomerular filtration rate, a measure of kidney filtration. Creatinine-based estimates read low in high-muscle individuals; cystatin C is the better measure here | Qualitative markers to track alongside the labs: * New or spreading small red vascular marks on lips, fingers, nail beds or inside the nose * Nosebleed frequency and duration, and any gum bleeding when brushing * Headache frequency and character compared with the pre-exposure baseline * Girth measurements and progressive-overload logs, as a cross-check on whether added size is doing work * Energy, training recovery and sleep quality, which drift first when red cell mass or iron status changes ## Emerging Research * **Trevogrumab with semaglutide for lean-mass preservation:** [NCT06299098](https://clinicaltrials.gov/study/NCT06299098), a Phase 2 trial in 1,005 adults with obesity testing trevogrumab, alone or with garetosmab, added to semaglutide. Primary endpoints include percent change in lean mass, fat mass and body weight. * **Bimagrumab with tirzepatide:** [NCT06643728](https://clinicaltrials.gov/study/NCT06643728), a Phase 2 trial in 252 adults with obesity or overweight, primary endpoint percent change in body weight. Together with the trial above, this is where the class is now being tested at scale. * **Taldefgrobep alfa in spinal muscular atrophy:** [NCT05337553](https://clinicaltrials.gov/study/NCT05337553), a Phase 3 trial in 269 participants with the primary endpoint a validated motor function score — a direct test of whether the class produces function, not only size. * **Apitegromab in facioscapulohumeral muscular dystrophy:** [NCT07435129](https://clinicaltrials.gov/study/NCT07435129), a Phase 2 trial in 60 participants extending selective myostatin blockade to a second muscular dystrophy. * **Evidence that could strengthen the case:** the delayed primate study of ACE-031 itself reports fiber-level growth and increased isolated muscle force in marmosets ([Cadena et al., 2026](https://pubmed.ncbi.nlm.nih.gov/41686840/)), the closest thing to functional confirmation the compound has. * **Evidence that could weaken the case:** pooled trials of the closely related bimagrumab show raised low-density lipoprotein and sharply increased muscle spasm, diarrhea and discontinuation ([Shao et al., 2026](https://pubmed.ncbi.nlm.nih.gov/42530342/)), and no effect on disease progression in inclusion body myositis ([Santos et al., 2025](https://pubmed.ncbi.nlm.nih.gov/39843353/)). * **Unresolved gonadal question:** persistent testicular abnormalities after long-term activin and myostatin blockade in mice ([Vaughan et al., 2021](https://pubmed.ncbi.nlm.nih.gov/33408083/)) have never been followed up in humans, and no current trial measures it. * **Detection science:** analytical methods now distinguish genuine ACE-031 from what grey-market vials contain ([Reichel et al., 2025](https://pubmed.ncbi.nlm.nih.gov/40312924/)), which also gives buyers a testable way to verify identity. ## Conclusion ACE-031 is a laboratory-built decoy protein that soaks up the body's own brakes on muscle growth. Given by injection, it enlarged muscle in both human trials that measured it, and it also increased bone density and reduced body fat. Those gains were real but modest, and they arrived without any matching gain in strength or walking ability — the pattern that has since repeated across every related compound. The reason development stopped is equally clear. The same breadth that made the decoy effective also removed signals that keep small blood vessels stable, and at the higher dose many participants developed clusters of widened vessels and nosebleeds. Whether those changes fully reverse was never established, and longer-term questions about red cell excess and fertility rest on animal work alone. The evidence base is thin and conflicted at its root: almost every human and animal finding was produced and reported by the company that owned the compound, and the analytical work on today's supply comes from laboratories whose mandate is to detect it. Beyond that, no legitimate product exists — nearly every vial tested contained a different protein entirely. So the honest summary is a compound with a demonstrated effect on muscle size, an unresolved and dose-related vascular harm, no evidence of functional benefit, and no verifiable supply. **[Top](#top) - [Benefits](#expected-benefits) - [Risks](#potential-risks--side-effects) - [Protocol](#therapeutic-protocol)**