Follistatin and ACE-031 both aim to increase muscle by blocking the myostatin pathway, which normally limits muscle growth — but they do it differently. Follistatin binds and neutralizes myostatin (and related factors); ACE-031 (a soluble activin receptor) acts as a "decoy" that soaks up myostatin and activins. Both are unapproved, with notable safety caveats.
At a glance
| Follistatin | ACE-031 | |
|---|---|---|
| Type | Myostatin/activin-binding protein | Soluble activin receptor (decoy) |
| Mechanism | Binds and neutralizes myostatin | Acts as a receptor decoy for myostatin/activins |
| Goal | Increase muscle growth | Increase muscle growth |
| FDA status | Not approved (research chemical) | Not approved |
| Safety note | Human evidence limited | Trials halted over vascular/bleeding safety signals |
| Sport status | Banned (WADA) | Banned (WADA) |
The bottom line
Bottom line: Two approaches to the same target — releasing the "brake" myostatin puts on muscle. Follistatin neutralizes myostatin directly; ACE-031 is a decoy receptor. Critically, ACE-031's development was halted over safety signals (including vascular/bleeding effects), and neither has established human benefit. Both are unapproved and banned in sport.
Frequently asked questions
What's the difference between follistatin and ACE-031?
Both target the myostatin pathway to promote muscle, but follistatin binds and neutralizes myostatin directly, while ACE-031 is a soluble activin receptor that acts as a decoy to soak up myostatin and activins.
Is ACE-031 safe?
ACE-031's clinical development was halted over safety signals, including vascular and bleeding-related effects. Neither it nor follistatin is FDA-approved, and human benefit for physique is not established.
Do myostatin inhibitors build muscle?
They aim to release the natural 'brake' (myostatin) on muscle growth, with striking effects in animals. Robust human benefit is not established, and these compounds are unapproved and banned in sport.
References
Combined peer-reviewed sources from both peptide guides. Inclusion is not endorsement.
- Haidet AM, Rizo L, Handy C, et al. Long-term enhancement of skeletal muscle mass and strength by single gene administration of myostatin inhibitors. Proc Natl Acad Sci U S A. 2008. Peer-reviewed study
- Barbe C, Bray F, Gueugneau M, et al. Comparative proteomic and transcriptomic analysis of follistatin-induced skeletal muscle hypertrophy. J Proteome Res. 2017. Peer-reviewed study
- Bielka W, Przezak A, Pawlik A. Follistatin and follistatin-like 3 in metabolic disorders. Prostaglandins Other Lipid Mediat. 2023. Peer-reviewed study
- Kozaki K, Ouchi Y. Activin/follistatin and atherosclerosis--a review. J Atheroscler Thromb. 1998. Peer-reviewed study
- Hansen JS, Plomgaard P. Circulating follistatin in relation to energy metabolism. Mol Cell Endocrinol. 2016. Peer-reviewed study
- Phillips DJ, de Kretser DM. Follistatin: a multifunctional regulatory protein. Front Neuroendocrinol. 1998. Peer-reviewed study
- Campbell C, McMillan HJ, Mah JK, et al. Myostatin inhibitor ACE-031 treatment of ambulatory boys with Duchenne muscular dystrophy: a randomized, placebo-controlled trial. Muscle Nerve. 2017. Peer-reviewed study
- Attie KM, Borgstein NG, Yang Y, et al. A single ascending-dose study of muscle regulator ACE-031 in healthy volunteers. Muscle Nerve. 2013. Peer-reviewed study
- Reichel C, Filip T, Gmeiner G, et al. Gel Electrophoretic Detection of Black Market ACE-031. Drug Test Anal. 2025. Peer-reviewed study
- Cadena SM, Bogdanovich S, Khurana TS, et al. ACE-031, a Soluble Activin Type IIB Receptor, Increases Muscle Mass and Strength in the Common Marmoset (Callithrix jacchus). bioRxiv. 2025. Peer-reviewed study
- Cadena SM, Bogdanovich S, Khurana TS, et al. ACE-031, a soluble activin type IIB receptor, increases muscle mass and strength in the common marmoset (Callithrix jacchus). PLoS One. 2026. Peer-reviewed study