YK11 is theorized to allow bodybuilders to inhibit the feedback loop in their body that limits how much muscle they can pack on via Myostatin inhibition.
The end result of this could be increased muscle growth potential that would otherwise be impossible to achieve.
In this article, I break down exactly what to expect from YK11, how it differs from other “traditional” SARMs, and what potential applications it may have.
Table of Contents
What Is YK11?
YK11 is a steroidal selective androgen receptor modulator (SARM) and Myostatin inhibitor that was popularized because of its potential to induct supraphysiological levels of Follistatin expression.
This SARM never passed the preclinical development stage and has never been tested on animals or humans.
While there is a decent amount of anecdotal information to reference due to its popularity in the bodybuilding community, the data itself is fairly limited, as only a minority of individuals are logging their blood work consistently, and even fewer are getting extensive testing done to establish exactly what effects YK11 had on their body.
One commonality among the majority of YK11 users are impressive increases in muscle growth, strength gains, improvements in body composition, with temporary natural Testosterone suppression being the most common obvious side effect.
Cellular studies conducted on YK11 suggest that it has an anabolic effect on muscle tissue and bone which is mediated through androgen receptor activation, as well as via its induction of Follistatin expression [R, R].
It is unclear if YK11 was abandoned in preclinical development, and if it was, what the reason was.
It is a very misunderstood compound which may have some very promising applications we have yet to learn about.
Is YK11 A SARM Or A Steroid?
It is classified as a SARM only because of the limited data that suggests it has selective activation of the androgen receptor [R].
SARMs are traditionally non-steroidal, whereas YK11 clearly has a steroidal backbone [R].
Anecdotally, YK11 seems to behave similarly to DHT derived anabolic steroids.
The term SARM can be applied relatively loosely in some contexts, and it should be noted that any compound that selectively activates the androgen receptor can technically be classified as a SARM, even if it blatantly belongs to another category of hormones entirely.
A good example of this is Trenbolone, which is consistently referred to in animal models for its tissue selective SARM-like effects [R].
YK11 Mechanism Of Action
YK11 binds to the androgen receptors in muscle and bone in a similar way to SARMs.
After binding to the androgen receptors, it exerts tissue selective anabolic activity.
It has a partial agonistic effect on the androgen receptor compared to dihydrotestosterone (DHT) [R].
As a partial agonist, YK11 only partially activates androgen receptors and will compete directly with endogenous Testosterone and DHT for receptor activation.
The result of this could theoretically be a decrease in muscle size and strength should YK11 displace endogenous Testosterone.
Of course, this would vary based on the dosage of YK11, the amount of endogenous androgens in the body, the amount of synthetic exogenous androgens in the body, and how YK11 actually works on the cellular level.
One of the other mechanisms through which YK11 facilitates its effects after binding to the androgen receptor is by inducing greater expression of Follistatin.
YK11 induces the muscle cells to produce more Follistatin, consequently inhibiting Myostatin in the body, which could then result in more overall muscle growth.
The anabolic capabilities of YK11 could be largely mediated by its induction of increased Follistatin production, and the extent to which this occurs remains unknown.
Despite YK11 having a traditional steroidal backbone, YK11 induced Follistatin expression while DHT did not [R].
The anabolic effects of YK11 were reversed with an anti-Follistatin antibody, thereby suggesting that the effect YK11 has on muscle growth is largely mediated via its induction of Follistatin.
To date, no other known anabolic hormone is capable of inducing Follistatin production the same way YK11 can.
Follistatin And How It Affects Muscle Building
Follistatin is a protein that acts as an antagonist to Myostatin in the body, and is arguably one of the most critical factors that will determine how muscular someone can become [R].
While Follistatin is naturally occurring in the body, it is theorized that by increasing these levels you could inhibit more Myostatin, which would consequently remove the limitations your body sets on muscle growth.
Myostatin inhibitors have been proposed by many to be the most promising new area of science in a bodybuilding context, as well as potentially better alternative treatment for muscle wasting diseases.
Follistatin was first popularized when it was discovered that it quadrupled the muscle size of Myostatin deficient mice [R].
Mice that lack the gene that creates Myostatin have approximately twice as much muscle mass as normal mice.
Mice that lack the gene that creates Myostatin and overproduce Follistatin simultaneously have approximately four times as much muscle mass as normal mice [R].
Follistatin increases muscle mass via another pathway as well that does not involve Myostatin inhibition, but what that pathway is remains unclear.
99.9% of Follistatin is fake, so I highly recommend that you DO NOT waste your money buying vials of Follistatin from research chemical websites.
It is always bunk, and companies often take advantage of the hype around it by selling it at obscenely high prices.
Myostatin And How It Affects Muscle Building
Myostatin is a protein in the body that acts as a regulator of skeletal muscle mass, limiting how much muscle the body can grow.
Interestingly enough, genetically gifted bodybuilders have been found to have very low levels of Myostatin in their bodies, which we can surmise is the reason why they have such a remarkable ability to pack on muscle.
Supposedly, Flex Wheeler in particular (one of the greatest bodybuilders of all time) was a participant in a study conducted in collaboration with the Department of Human Genetics at the University of Pittsburgh involving 62 men.
All of these men made unusually large gains in muscle mass in response to strength training, and is why they were included in the study.
When the results came in, Flex Wheeler was revealed to be one of only nine extreme responders that had a very rare Myostatin mutation at the exon 2 position on the gene.
This is the rarest myostatin mutation found in humans, and the result of this mutation is a much larger number of muscle fibers than the average male.
What Is A Myostatin Inhibitor?
As Myostatin keeps your body from growing too much muscle, a Myostatin Inhibitor would be a compound that could inhibit Myostatin from acting on muscle cells, thereby allowing you to greatly surpass your previous muscle-building threshold.
YK11 is a Myostatin inhibitor because it induces greater levels of Follistatin expression.
In theory, by increasing Follistatin expression YK11 could indirectly inhibit Myostatin and facilitate anabolic effects in the body far greater than would be possible otherwise.
There are no animal or human trials to definitively state that YK11 has any effect whatsoever, however, in its cell-based studies and in hundreds of anecdotal logs it has exhibited a fairly substantial anabolic effect on muscle growth [R].
The mechanism by which YK11 facilitates its effects is different than the more mainstream SARMs, Steroids, or HGH.
Because of this, it is theorized that YK11 could be added to any performance enhancing cycle for additional muscle growth and anabolic synergy.
By facilitating an increase in Follistatin expression, YK11 will inhibit Myostatin, which may allow the user to surpass their genetic limit in regards to the accrual of muscle mass.
YK11 upregulated osteoblastic proliferation in a cellular study [R].
Osteoblasts are cells that develop bone.
By rapidly increasing the number of osteoblasts, YK11 may be able to help prevent and reverse bone wasting diseases.
This function makes YK11 a promising SARM for osteoporosis and other androgen deficiency related diseases.
Anecdotally, YK11 seems to produce a hardening effect similar to certain DHT derivatives.
YK11 Reviews (Anecdotal/Recreational Reports)
YK11 is reported to produce lean, dry gains.
With the exception of hair loss, reports of other side effects from YK11 are typically less prevalent than with the more mainstream very suppressive SARMs.
YK11’s chemical structure differs greatly from that of SARMs and resembles the chemical structure of an anabolic steroid.
It may be more accurate to say that YK11 is a steroidal SARM, rather than to say it is a non-steroidal SARM.
Unfortunately, it is pretty unclear exactly what it is as it is very new on the scene, and most of the conclusions being drawn about this compound are just based on personal opinion rather than true science.
One thing we do know is that the unique effect YK11 has on Follistatin expression is completely unlike any SARM.
Anecdotally, YK11 exhibits a blatant anabolic effect and has muscle building potential, however, it doesn’t seem to produce any mind blowing muscle growth that would not be achievable with other far more thoroughly studied anabolic agents.
Personally, I have yet to see one person take their physique to a new level solely from YK11, and it certainly has not produced any Flex Wheelers.
With that being said, without human trials there is no way to actually assess how much YK11 can inhibit Myostatin in humans (if at all), and if there is a dosage that could equate to the same level of Myostatin inhibition that a genetic anomaly with a gene mutation has.
YK11 isn’t necessarily better or worse than any other SARMs, but this is because it operates via a completely separate mechanism of inducing muscle growth.
Because YK11 induces muscle growth via a completely separate pathway than other anabolic steroids or SARMs, it would be more productive to figure out what would work best alongside it, or if it is even worth exploring in the first place, rather than if it’s stronger or weaker than other anabolics that induce muscle growth in a totally different manner.
YK11 Side Effects
YK11 suppresses natural testosterone levels in a dose-dependent manner the same way anabolic steroids and SARMs do [R].
This occurs via the suppression of luteinizing hormone (LH) and follicle stimulating hormone (FSH) through the Hypothalamus-Pituitary-Testes-Axis.
While there have been no studies to test this specifically, anecdotal reports with blood work confirm that YK11 is suppressive.
Anecdotally, YK11 has exhibited transient increases in liver enzymes.
Anecdotally, reports of hair loss from YK11 are fairly common.
Joint And Tendon Weakness
Anecdotally, some users have reported joint pain while using YK11.
Myostatin is expressed in tendons and appears to play an important role in tendon maintenance.
Myostatin deficient mice have been found to have weak and brittle tendons [R].
This suggests that YK11 may have a negative effect on tendon strength as a consequence of Myostatin inhibition.
Users report blatantly increased levels of aggression on YK11.
10 mg per day is the most common YK11 dosage used in a performance enhancing context.
Some users report using daily dosages as high as 30 mg per day.
The general consensus seems to be that 10 – 15 mg per day can produce desirable outcomes with a relative lack of side effects in men.
There is no set in stone dosing protocol for YK11 and all current conclusions about effective dosages have derived entirely from anecdotal reports.
The half-life of YK11 is unknown, so splitting the total daily dosage up into several micro-doses per day would likely yield better outcomes with more stable blood serum concentrations.
YK11 PCT (Post Cycle Therapy)
YK11 will suppress natural testosterone levels, so a PCT phase may be warranted.