YK-11

The honest state of the evidence is that this entire reputation comes from a handful of in-vitro (cell-culture) papers from one research group: YK-11 acts as a gene-selective partial AR agonist in reporter assays, and in mouse C2C12 myoblasts it induced the myogenic regulatory factors and the protein follistatin — and because follistatin antagonizes myostatin, this cell-culture follistatin induction is the sole basis for the 'myostatin inhibitor' marketing claim.

Later in-vitro work showed YK-11 also pushed mouse osteoblast cells toward differentiation. That is the whole efficacy pyramid: cell culture.

There are NO animal studies showing it builds muscle or extends anything, and there are NO human trials, case series, or pharmacokinetic data establishing a dose, a benefit, or a safety margin in people.

The only in-vivo study is a rat experiment that found YK-11 caused oxidative stress and mitochondrial dysfunction in the hippocampus — a toxicity signal, not a benefit.

Against that thin and theoretical efficacy stand concrete risks: grey-market SARM products are routinely mislabeled (a JAMA analysis found most contained the wrong drug, the wrong dose, or unapproved drugs entirely); SARMs as a class are linked to drug-induced liver injury in published case reports; oral steroidal androgens carry HPTA-suppression and androgenic risk; and YK-11 is banned by WADA, so any tested athlete will fail.

This is a research chemical with no approved use, not a dietary supplement. The score reflects an evidence base that does not rise above mouse cell culture, with no efficacy demonstrated in any living animal or human and real safety and mislabeling concerns.