Other Name(s): YK11, Myostine
Molecular Name: C25H34O6
Half Life: 6-10 hours, depending on individual
YK11, also known as Myostine, is considered one of the strongest SARMs on the market. In fact, it’s so strong and has comparable anabolic activity to steroids that it may actually be a synthetic steroid that was mislabeled a SARM in the first place.
YK11 was first studied by Japanese researcher Yuichiro Kanno in 2011. It was found to be a partial agonist of the Androgen Receptor (AR) with gene-selective properties, leading researchers to suggest that the compound is a SARM. 
To date, limited studies have been undertaken, although preliminary findings in vitro on muscle cells are very promising. Initial studies suggest that YK11 may have greater muscle building effects than those of DHT and a propensity to act as a myostatin inhibitor.
How it works
As a relatively new compound, exactly how YK11 works to improve lean muscle mass in humans can only be discussed based on intial in vitro studies.
However, what we do know is that YK11 may be a Myostatin blocker – essentially allowing users to reap continuous gains without stalling and requiring a break in a cycle.
Myostatin is a protein that is released to limit muscle growth to ensure they do not get ‘too large’. It is found predominantly in skeletal muscle, and studies show that individuals with a gene mutation that limits Myostatin production are both stronger and more muscular than those with normal amounts.
YK11 may help to inhibit the production of Myostatin in muscles by attaching itself to the Androgen Receptor. From there, it may induce muscles to create more Follistatin, which in turn limits the levels of Myostatin, allowing increased muscle growth beyond genetic capability.
The confusion over whether Myostatin is a SARM or a steroid lies in the naming convetions (or lack thereof) in relation to newer compounds. Kanno, the original Japanese researcher, discovered that YK11 works via the androgen receptor, which is why he initially claimed it to be a SARM.
Newer research suggests that the backbone of YK11 is identical to those of steroids. In reality, we won’t know for sure until more studies are conducted.
I just started running YK11 three days ago, and so far this stuff has made me feel like a complete animal in the gym. It’s very good stuff…makes you very dense feeling and gives you a ton of energy in the gym.
There are 3 primary benefits that have been observed in both initial studies and user-reported reviews.
- YK11 may block Myostatin, allowing continues lean body mass gains
The primary benefit of YK11 and the reason it shows huge promise in the bodybuilding world is its potential to activate more Follistatin in muscles, subsequently blocking the production of Myostatin. By blocking Myostatin, a user could potentially unleash huge gains with continuous muscle growth. 
- YK11 may be comparable to testosterone in its ability to build strength in muscles
It’s a commonly held belief that while SARMs produce less negative side effects than testosterone, they’re also less effective at creating an anabolic effect in muscle growth.
Initial studies  show that muscle cells produce more anabolic factors when exposed to YK11 than they do when exposed to DHT (testosterone). This suggests that YK11 is potentially more powerful than testosterone at producing impressive gains with less side effects than steroids.
- YK11 shows potential for fast, large gains
Many users report seeing results from YK11 in as little as a single week of use, with the amazing results after an eight-week cycle.
YK11 has only been tested in vitro – meaning that it has been tested on cells in a petri dish rather than on live animals or humans – where it has shown great promise in building lean muscle mass. However, this also means that until animal or human trials are conducted, we will not know what the potential side effects may be.
Anecdotal evidence from individuals who have cycled YK11 suggests that for those prone to hair loss, shedding may occur. Other users have noted zero hair loss, so it may be a case-by-case situation based on each individual.
Other anecdotal evidence suggests that mild acne may be a side effect of YK11, but this also disappears after a few weeks or once the cycle is complete.
It has also been suggested that YK11 may cause mild, reversible liver damage. This means that any damage caused is repaired by the body once the cycle is complete.
User reviews suggest that the ideal human dosage for YK11 is 2-5mg twice per day for eight weeks (a total of 5-10mg per day for men).
Anecdotally, some users suggest increasing the dosage to 20mg per day in total over the course of a cycle, although it’s best to start at a lower dosage and find your sweet spot.
5-10mg total per day split into two doses.
0.5-2mg total per day split into two doses.
There have been quite a few anecdotal reports from users who have stacked YK11 with RAD140 with incredible results.
Users report increased strength and an increase in lean muscle mass similar to testosterone results but without the water bloat. It works great for users looking to bulk with lean, dry gains.
- RAD140 (Testolone) – 15-30mg
- YK11 (Myostine) – 5-10mg
“I’m no Doctor or Scientist here, but I know what works. This stack (YK11 and RAD140) is absolutely killing it!! Shit, I may run it out 12 weeks instead of just 8 weeks. The gains just keep coming, I don’t want them to end anytime soon!!”
– John Doe
Where to Buy YK 11 Online
YK11 can be easily and legally purchased online for research purposes, which means there are ample companies to choose from. However, as the compound is yet to be approved for human consumption, the SARM industry is unregulated and it’s important to do your due diligence in finding a reputable supplier.
A recent ban has forced some reputable distributors to shut down. The best recommendation we can give is sarms4you.com, which offers worldwide deliveries, including the US.
Although YK11 has not been officially clinically trialed or studied on humans or animals, the anecdotal evidence from real users is hugely compelling. Many users note feeling stronger, more muscular and with better pumps and dry bulk even comparable to testosterone.
Additionally, users have reported minimal or mild side effects compared to the benefits gained. They also report faster gains than usual, with most stating that they noticed changes in their bodies within a week of use.
However, as with all SARMs (and especially with compounds that have not been subjected to rigorous animal and clinical trials), anecdotal evidence should be taken with a grain of salt. Until human trials have been undertaken, there is no way to know exactly what YK11 can do to the majority of people or if it is safe long term.
Overall, YK11 shows great potential to create huge gains outside of genetic capability, and existing user reviews are very promising. But, more studies are needed to understand the efficacy and long term effects of this compound.
“Pumps are still as good as when they really kicked in last week. Must have been 5 guys in the last 2 days asking me what the hell I’m taking, so it must be working. Legs are really feeling out, calves to. Wife told me today my calves look bigger and she never says anything unless it noticable.”
To date, there have not been any clinical human or animal trials and YK11 is not FDA approved for human use. However, existing studies and user-reported reviews are promising, and side effects look to be minimal.
Anecdotally, some users report noticing changes in their physiques in as little as one week. However, for best results, an 8-week cycle is recommended.
Most user-reported reviews suggest taking YK11 for 8 weeks before taking a miniPCT of 4 weeks.
As YK11 does not appear to remarkably affect testosterone levels, it should be safe for women.
The suggested dosage of YK11 is 10-20mg per day, split into two doses. We suggest trialing different doses to find your sweet spot by starting at the lower dose before ramping up.
Yes. As it is mildly hepatotoxic (damaging to the liver), we strongly suggest taking a miniPCT for 4 weeks to ensure hormone levels are back to normal after an 8-12 week SARM cycle.
Most users report taking their dose of YK11 in a split dose, 10-hours apart.
Yes, YK11 is legal to purchase from a number of research companies for research purposes. It is not yet sold for human consumption.
There is some disagreement over whether YK11 is a SARM or a steroid. The original researcher suggests that it is a SARM. Others online suggest that the molecular structure mirrors that of a steroid. Until further research is done, a conclusive answer cannot be provided.
 Kanno, Yuichiro et al. “Selective Androgen Receptor Modulator, YK11, Regulates Myogenic Differentiation of C2C12 Myoblasts by Follistatin Expression.” Biological and Pharmaceutical Bulletin Volume 36 (2013) Issue 9 Pages 1460-1465 Web. 29 May. 2018.