The verdict
Our read at a glance.
Whether inducing follistatin in cultured mouse myoblasts predicts anything about muscle growth in a human being.
- The signal
- In C2C12 mouse myoblast cultures, YK11 induced follistatin expression where DHT did not, and the myogenic differentiation it produced was reversed by an anti-follistatin antibody. That is the whole efficacy literature: one cell-culture mechanism paper. Separate anti-doping work has characterized its metabolites in vivo, which tells us how to detect it, not whether it works.
- The unknown
- Everything past the petri dish. There is no animal efficacy study establishing that it builds muscle in a living organism, no human study of any kind, no established dose, and no pharmacokinetic data. Its structure is steroid-derived rather than non-steroidal, so androgenic and hepatic effects cannot be assumed away by calling it a SARM.
- Our read
- The gap between evidence and marketing is about as wide as it gets on this Watchlist. One paper, in mouse cells, on a mechanism, sold as a muscle-building compound with a dosing protocol. Compare it against ACE-031, which actually reached a controlled human trial and still got stopped.
The mechanism
How it works.
Safety & regulatory boundary
The consequential part.
Not approved for human use anywhere; the anti-doping literature describes it explicitly as an experimental drug candidate and a non-approved substance for humans. SARMs as a class are prohibited in sport and have been the subject of FDA warnings about liver injury and cardiovascular risk. Sold as a research chemical, so identity and purity are unverified per unit.
What's next
What we're watching.
Any animal efficacy study, any human pharmacokinetic or safety data, and independent replication of the follistatin finding outside the originating group.
Context
Why this is discussed.
The pitch combines two attractive stories at once, an androgen receptor modulator and a myostatin inhibitor, and it is sold openly as a capsule or injectable.
The evidence base
4 cited references.
Regulatory & labels2
World Anti-Doping Agency · Effective 2026-01-01
U.S. Food and Drug Administration · Current FDA page
Indexed literature (PubMed)2
Kanno Y, Ota R, Someya K, Kusakabe T, Kato K, Inouye Y (Biol Pharm Bull) · 2013
Piper T, Dib J, Putz M, Fusshoeller G, Pop V, Lagojda A, Kuehne D, Geyer H, Schaenzer W, Thevis M (Drug Test Anal) · 2018
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