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YK11: What is it Used For? + Safety & Side Effects

Written by Mathew Eng, PharmD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Mathew Eng, PharmD | Last updated:

Many bodybuilders think YK11 is the key to achieving fast muscle gains with few side effects. YK11 is promoted as a super-SARM, but this drug is unapproved, poorly understood, and probably dangerous. What are the risks? Learn more here.

Disclaimer: We strongly recommend against using YK11 for any reason. This is an unapproved drug which has caused serious adverse effects in the limited available studies. Some of our readers who were already taking the drug requested that we commission a post on it, and we are simply providing information that is available in the clinical and scientific literature.

Due to reported toxic incidents, the FDA has issued letters warning against the use of YK11 and similar research chemicals [1].

What is YK11?

Steroid-SARM Hybrid

YK11 is a new synthetic steroid based on 5-α-dihydrotestosterone (DHT), a hormone naturally found in the human body. DHT is a stronger form of testosterone that targets androgen receptors in the prostate, sex organs, hair, and liver.

YK11 is gaining interest from bodybuilders, who believe it can help them quickly build muscle with minimal side effects—a belief which is not founded in the available science. The YK molecule has more in common with steroids than SARMs, although it’s often mistakenly labeled as a non-steroidal SARM [2].

According to preliminary cell studies, YK11 may increase muscle mass and enhance bone health [3, 4].

Some bodybuilders who have experimented with YK11 report great muscle gains and fat loss with minimal side effects. However, there are currently not even any animal studies of YK11 and its safety profile is unclear. It is extremely dangerous to use research chemicals which are so poorly studied. We strongly recommend against using YK11 for this reason.

Along with all steroids and SARMs, YK11 is banned in professional sports by the World Anti-Doping Agency [5].

YK11 is a synthetic steroid with SARM properties, promoted to quickly build muscled. It’s banned in professional sports and not well researched; because of its incomplete safety profile and unknown side effects, it is considered extremely dangerous to use.



  • May increases muscle growth
  • May boost fat-burning
  • May increase bone strength


  • Not enough data to know whether it’s safe or effective
  • Steroidal structure (not a typical SARM)
  • Testosterone suppression
  • No human or animal studies
  • Long-term risks unknown
  • Insufficient safety data
  • May have additional unknown side effects

Is It a SARM?

Bodybuilders and researchers sometimes refer to YK11 as a SARM (selective androgen receptor modulator). This may be misleading as other SARMs differ from YK11.

YK11 is a steroid made by altering the chemical structure of DHT. In contrast, all other SARMs have a nonsteroidal structure. YK11 and SARMs work differently in the body and may have different side effects [2, 6].

Cell studies do show that YK11 has a selective effect on androgen receptors. This means the SARM label does technically describe YK11 [2].

Because this class of drugs is new, no established naming convention exists.

Based on its activity and chemical structure, it may be more appropriate to call YK11 a synthetic steroid rather than a SARM.

How Does It Work?

The chemical structure of YK11 is similar to DHT, and it binds to androgen receptors in a similar way. DHT is a naturally occurring hormone in the body crucial for hair growth, prostate health, and proper development in puberty.

Some bodybuilding resources state that YK11 is one of the strongest SARMs on the market. However, research revealed that YK11 only partially activates androgen receptors. Such limited activation increases the activity of catabolic (muscle-degrading) genes [2].

A recent cell study uncovered YK’s unique muscle-building mechanism: increasing follistatin levels. Follistatin is a naturally occurring protein that suppresses myostatin, which otherwise prevents muscles from getting too large. In comparison, no other SARMs show myostatin inhibition [3].

YK11 may also increase bone growth by affecting a DHT-like pathway, according to other cellular studies. However, it is unclear whether this mechanism would transfer to living animal or human systems [4].

Some scientists have hypothesized that YK11 may work by mimicking DHT and activating androgen receptors in muscles and bones. However, there is currently not enough research to be sure.

YK11 is Currently Being Investigated For:

1) Muscle Size

According to cell-based studies, YK11 boosts muscle growth by increasing follistatin levels and thus inhibiting myostatin [3].

YK11 has not been studied in animals or humans. Thus, there isn’t sufficient evidence to justify using YK11 for any reason.

YK11 may boost muscle growth by inhibiting myostatin. There are no human or animal studies to confirm this.

2) May Strengthen Bones

Sex hormones play an important role in maintaining healthy bones. YK11 may be able to bind to androgen receptors in bone tissues and increase bone strength, similar to steroids and SARMs.

YK11 increased levels of activated PKB (protein kinase B) in cells; activated PKB sends signals to increase bone growth [4].

YK11, like other SARMs, is currently being investigated for potential uses in bone health. This could make it relevant in older people who struggle with both muscle and bone frailty; however, we must note again that there are currently no human or even animal studies to back this up [7].

YK11 is being investigated for its potential to help prevent fractures, especially in the elderly, but such research has not yet even progressed into animal studies.

YK11 for Bodybuilding

User Reports

Remember that there have been no human or even animal studies on YK11. We are providing some user experiences here, to discuss why some people take YK11 and to explore anecdotes of possible adverse effects. None of this can replace proper clinical testing.

New SARMs are always a hot bodybuilding topic.

Positive reviews of YK11 report that it greatly increases muscle mass in as little as a week. However, these claims are clouded by the fact that people use different dosages, cycle lengths, or stack YK11 with other SARMs. Other users report no benefit at all.

Some state that YK11 offers similar results to other SARMs. Many would prefer taking a SARM that is backed up with better research than YK11 if the results are similar.

Bodybuilders have experimented with YK11 in both bulking and cutting. Some users claim that it works great both ways by building lean muscle mass and burning fat.

All these claims remain purely anecdotal. Users must be cautious as the information on YK11’s safety and long-term effects is scarce, and no human studies have been conducted. It is extremely dangerous to use completely untested experimental compounds like YK11. We do not recommend taking YK11 for any reason.

Some bodybuilders tout YK11 as a relatively safe option for building lean muscles and burning fat, but others report no benefit. Furthermore, no studies are available to support these claims, and we don’t know whether YK11 is safe or effective.


Anecdotal reports suggest the most common dosage is 10-15 mg, divided into two daily doses. However, there is no safe, effective dosage of YK11 because no high-quality clinical trials have determined one.

Bodybuilders report using doses between 5 mg and 30 mg, cycled for 4 to 8 weeks. Women report taking 0.5 – 2 mg per day. This is not based on scientific data of any kind, as such data is unavailable.

Most users take YK11 by mouth while some have used muscle injections.

Some users report stacking with LGD-4033 or RAD140 and using a lower dose of YK11, typically 5-10 mg per day. Using even one unapproved research chemical at a time is considered dangerous; using more than one is even more dangerous. Not only do we not know enough about the safety profile of each of these drugs; we also don’t know how they might interact in the body. We do not recommend using any research compounds alone, let alone together.

There is no safe, effective dosage of YK11 because no sufficient studies have been performed to find one.

In Professional Sports

Anabolic agents, including all SARMs, are prohibited in professional sports by the World Anti-Doping Agency. No matter how YK11 is labeled – as a SARM or synthetic steroid – it is banned in competitions [5].

The doping test is currently in use and can detect YK11 metabolites up to 2 days after use [8].

Limitations and Caveats

The current research on YK11 is scant. It has not been studied in animals or humans. All cellular studies on YK11 have been done by one group of researchers from Japan.

YK11’s safety and effectiveness can only be evaluated once more research is done. It is extremely dangerous to use an untested, unapproved research chemical that we know almost nothing about. We strongly recommend against putting your health on the line in this way.

Side Effects

Unknown Safety

YK11 has only been studied in cells so far. There’s no clinical information on side effects. Not even animal studies have been carried out yet.

In a cell study, YK11 increased the levels of follistatin. High follistatin may increase the risk of esophagus, stomach, skin, and prostate cancer. On the other hand, a human study suggests that high follistatin may be beneficial for breast cancer [9, 10, 11, 12, 13].

The chemical structure of YK11 is very similar to other steroids that are toxic to the liver. YK11 may have toxic effects on the liver as well [14].

Theoretically, it may also affect the prostate, hair growth, vocal cords, and other organs.

No clinical or animal trials have examined the safety of YK11. It increases follistatin, which may raise the risk of certain cancers. Other steroid-like side effects are possible.

Beyond the Science

Given the limited research, the bodybuilding community online has waved a few red flags and reported some of the typical steroid side effects for YK11. These include:

  • Increased aggression
  • Joint pain
  • Low energy
  • Mild testosterone suppression
  • Hair loss
  • Mild acne

YK11 is potentially toxic to the liver, and mild testosterone suppression is possible. To be on the safe side, almost all bodybuilding resources recommend post-cycle therapy (PCT) after a cycle of YK11. Common PCTs include Nolvadex (tamoxifen) and Clomid (clomifene).

Bodybuilders have reported side effects such as aggression, joint pain, fatigue, hair loss, and testosterone suppression. Most resources recommend PCT after each YK11 cycle.

Buy YK11

There are vendors who sell YK-11 in the United States.

We strongly recommend against using YK11 because of the total lack of available research into its effects on humans or even animals. Speak to your doctor about safe and effective ways of achieving your health goals.


YK11 is a new steroid-SARM hybrid. It has a steroid structure and the selectivity of non-steroidal SARMs. So far, only cell-based studies confirmed it can build muscles via myostatin inhibition.

Users report major gains for bulking and cutting cycles (4-8 weeks) that few other SARMs can par with. On the downside, YK11 may cause testosterone suppression, joint pain, and hair loss. According to most experienced users, post-cycle therapy is a must.

Despite its promising effects, both animal and human studies are needed to determine the safety and effects of YK11.

About the Author

Mathew Eng

Mathew Eng

Mathew received his PharmD from the University of Hawaii and an undergraduate degree in Biology from the University of Washington.
Mathew is a licensed pharmacist with clinical experience in oncology, infectious disease, and diabetes management. He has a passion for personalized patient care and believes that education is essential to living a healthy life. His goal is to motivate individuals to find ways to manage their chronic conditions.


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