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YK11 – Side Effects, Benefits & Usage | Comprehensive Guide


What is YK11?

YK-11 is one of the most unusual and fascinating SARMs out there. It’s a 19-Nor (Nandrolone) family steroidal SARM that’s also meant to be a Myostatin inhibitor.

On paper, these characteristics make it a very strong and dynamic molecule that can be exploited to break through plateaus and overcome genetic limitations.

Unfortunately, despite its intriguing features, YK-11 has never been tested, and we have very little anecdotal knowledge about it. In truth, YK-11 was only investigated in test tubes and never on rats or primates, as it never made it to in vivo pre-clinical studies.

This article is a comprehensive guide on YK11 based on the latest scientific data and the careful analysis of hundreds upon hundreds of anecdotal reports and experiences online. Enjoy.


YK11 is most well known for its purported ability to inhibit myostatin – a protein that limits the growth of muscle cells. Thus YK11 is almost always stacked with other SARMs in order to leverage this unique property.

But as a 19-Nor derivative, and a non-steroidal SARM, it still holds many benefits:

Myostatin Inhibition [1][A]

Myostatin is a protein that regulates the growth of muscle cells, or more so, prevents it.

From an evolutionary aspect, it makes sense why our body has developed such a detrimental trait to our gains, an overly muscular body would be inconvenient for survival. 

The way YK-11 inhibits myostatin is by causing a spike in the production of Follistatin, an antagonist to Myostatin.

This image of genetically engineered rats from a study that researched Myostatins and Follistatins’ impact on muscular development shows exactly how significant their role is.

Comparing mice and their results from a Myostatin and Follistatin study.

The graph above is great at showing what low myostatin can do for a rat. And as much as we all want to be like the rats in the middle or right, we’ve not been genetically engineered (at least not most of us).

So for now, YK11 represents the only possible way, be it still in its early research phases, to achieve lower myostatin levels and surpass genetic limitations and plateaus.

Muscle Growth [2][A]

It is unclear how much muscle you can put on using YK-11 as a standalone compound as it’s usually always stacked with other drugs. This makes it hard to pinpoint exactly how much muscle gained was due to YK-11.

What we do know is, YK-11 is highly anabolic and it will significantly increase muscle mass. It’s often used as a secondary, or “wingman” compound since it is thought that by blocking myostatin, YK11 boosts the muscle-building potential of whatever it is combined with.

Strength & Performance [A]

When it comes to strength gains YK-11 is somewhat of a double-edged sword. After all, it’s a 19-Nor derivative, and these chemicals are known to boost strength, aggressiveness, and performance.

Unfortunately, YK-11 frequently causes stiff joints as a result of myostatin inhibition, a side effect that might jeopardize strength development.

Fat Loss [A]

Low levels of myostatin are linked to a reduction of fat mass, so if YK11 is indeed an effective myostatin inhibitor then it will help with losing more fat.

Bones and Joints [3][A]

All SARMs strengthen and densify your bones, and YK-11 is no exception.

But, when taking YK-11, many people report that their joints feel excessively weak and stiff. This makes sense because myostatin inhibition is linked to the deterioration of joint and ligament health.

This negative effect on joints puts athletes at an unfavorable predisposition to injuries during YK11 cycles.

Recovery [A]

You will recover significantly faster on YK-11, but the true extent of the increase in recovery is unknown. Although many users experience a level of recovery that no other SARM can equal. That’s yet another indication that YK-11 is a potent myostatin inhibitor.

Aesthetics [A]

When combined with another compound YK-11 accumulates a lot of growth and blows you up while also keeping you relatively lean and free from any water retention.

It is often compared to Winstrol and Masteron (much like we compare S-23), and cutting cycles using YK-11 are effective at really bringing out definition. The pumps on it are amazing, and that 3D look is pretty much solidified once you get on this SARM.

Side Effects

Testosterone Suppression [A]

It is unclear whether YK11 causes suppression like most SARMs or a complete shutdown like most AAS. Some users experience very mild suppression while others experience severe suppression.

If it is stacked with other SARMs or oral anabolics it will probably cause a complete shutdown of endogenous testosterone production, and a testosterone base along with a PCT are highly recommended if you plan to run it.

Testosterone suppression or shutdown can result in:

  • Decreased libido
  • Weaker erections
  • Lethargy
  • Lack of motivation
  • Feeling tired all the time 
  • Irritability
  • Testicular pain
  • Testicular atrophy

Your SHBG will also be reduced during a YK-11 cycle. This will raise your free testosterone levels, which will boost your libido, motivation, and overall well-being during the cycle, but only if you have a testosterone base.

Cholesterol [A]

YK-11 will cause dyslipidemia. By the end of your cycle, your HDL cholesterol will be considerably lower and your LDL cholesterol higher.

YK-11 is considered to be harsher on your lipid panel than most SARMs, and the effects are comparable to that of some oral steroids.

To measure the extent of the damage caused by this side-effect you will have to do bloodwork. Your cholesterol levels don’t impact how you feel day to day so you would have no other way of knowing.

Liver Toxicity [A]

YK-11 is a methylated oral AAS, unlike the other SARMs. This means that YK11 is significantly more liver toxic than other SARMs. Heaps of anecdotal bloodwork prove this to be the case.

Androgenic Side Effects [4][A]

While YK-11 is not a DHT derivative, many people still report androgenic side effects like hair loss, acne and aggression.

Other Side Effects [A]

Keep in mind that because this SARM is used so infrequently, there may be other adverse effects that we are unaware of, but the following side effects can occur in anybody who takes SARMs and disrupts their hormonal balance:

  • Gynecomastia: Growth of breast tissue in males. Caused by an imbalance between estrogen and testosterone. Men who have had pubertal gynecomastia are at a greater risk of developing it on a YK-11 cycle, otherwise, it is very rare.
  • Insomnia: Very unpredictable and easily dealt with and mitigated.

How to Take YK11

Take YK11 at 5-10 mg/day for 4-8 weeks. Since the half life is unknown, split the dose in three thirds. Take it once in the morning, once at noon, and once before bed. This way you make sure there are stable levels throughout the day.

YK11 works best when taken with another SARM. Its ability to inhibit myostatin is very synergistic with other compounds and acts as a “wingman” and amplifies the anabolic potential with whatever compound you stack it with.


The optimal YK11 dose has been shown to be 5-10 mg/day across the anecdotal data. Going over 10 mg/day will lead to a disproportionate increase in side effects to benefits, so keep the doses in that 5-10 mg range.

Half Life

The half-life of YK11 is still unknown as it is yet to reach pre-clinical or clinical trials and be tested on humans.


YK11 can be stacked with any other SARM. But no more than just one at a time. You can choose to add other chemicals that boost performance through other pathways, like MK677, Stenabolic, or Cardarine – depending on the objective of the cycle.

How to take it with other SARMs:

  • Start YK11 at the start of your cycle at 5mg, and at the 4-week mark increase it to 10mg
  • Add YK11 at the 4-week mark of your SARM cycle and run it for the remainder of the cycle at 5 or 10 mg/day

Myostatin build-up is the main reason why SARM cycles are typically 8 weeks long, so the idea is to introduce YK11 halfway through in order to intercept and cancel out the built-up myostatin.


YK11 is a very promising compound, and definitely the only one of its kind. Though very under-researched, many users swear by it and claim that it 100% inhibits myostatin. Unfortunately testing myostatin levels is very expensive, and very hard, so we don’t have a conclusive answer (yet). 

Remember, when it comes to SARMs and PEDs in general – less is always more! Do blood work, and cycle responsibly.


4. Androgenic Side Effects

  • (17α,20E)-17,20-[(1-methoxyethylidene)bis(oxy)]-3-oxo-19-norpregna-4,20-diene-21-carboxylic acid methyl ester (YK11) is a partial agonist of the androgen receptor [repeating]

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