Summary
Why Was Development Stopped?
In 2013, development was halted due to mild but concerning side effects, especially:
Bleeding tendencies (epistaxis, gum bleeding)
Vascular side effects—myostatin has roles in blood vessel formation and maintenance
Elevated liver enzymes (in some cases)
No life-threatening events occurred in trials, but regulatory and safety concerns paused
progress.
Summary of ACE-031:
Action: Myostatin inhibition
Therapeutic use: DMD, DMA, cachexia, sarcopenia
Recreational/ Off label use: Muscle growth, Reduction of tissue growth limits
Effects: Increased: Lean tissue and strength, Reduced Fat mass
Risks: Vascular side effects – Capillary damage and restructuring, EPO stimulation, bleeding, Increased BP, Increased RBC, elevated liver - enzymes.
Development: Halted in humans after phase 1 trials but is still researched in animal models.
Comparison of ACE-031 to YK-11
This to me is one of the most interesting comparisons of compounds due to the fact their potential is so high being that they are myostatin inhibitors. Although the primary purpose of both is identical (myostatin inhibition) their mechanism of action is very different.
ACE-031 is directly myostatin binding acting as a decoy, where as YK-11 is a steroidal SARM that induces follistatin which in turn will inhibit myostatin production. A key thing to note with the YK-11 is the fact it never underwent any human trials and was completely discontinued, where as ACE-031 has undergone phase 1 human trials and is still currently being used within animal models. Part of this is to do with the fact that ACE-031 has had legitimate intention of use for medical conditions where as YK-11 was only ever used within off label research and bodybuilders.
A brief comparison of the two will show that ACE-031 has a much faster onset time than YK-11 along with a potentially safer side effect profile (however neither are approved for human use and come with some pretty red flag side effects).