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MK-2866 (Ostarine) Benefits, Side Effects & Safety Information

Published: 13th May 2018. Last updated: 21th July 2019.

Shaun Ward MSc ANutr

Staff Writer


Ostarine, also known as MK-2866, is the most popular type of selective androgen receptor modulator (SARM) developed by GTX Incorporation.

The initial idea behind the drugs creation was to treat conditions associated with aging, such as sarcopenia and osteoporosis.

However, as ostarine is commonly compared to, and termed a “steroid-like” compound, it is becoming very popular amongst athletes and gym-goer’s to assist with training adaptations, and improve physical performance and appearance.

As SARMS are androgenic drugs, they are able to influence various biological processes such as the development and maintenance of muscle and bone tissues.

Ostarine has recently began Phase 3 clinical trials for the prevention and treatment of muscle wasting in patients with lung cancer during chemotherapy.

Does MK-2866 Work?

Ostarine exerts its effects by binding to and activating androgen receptors that are present on the surface of many cell tissues.

Upon binding, it can activate transcription factors that attach to certain DNA sequences called “androgen response elements”, upregulating the production of genes and proteins involved in muscle and bone metabolism.

This is the same process by which testosterone and steroid use has its dramatic effects.

However, what is unique about SARMs such as ostarine is that not only do they directly activate muscle androgen receptors, but they are also able to simultaneously inhibit the action of androgen receptor pathways in non-target tissues.

In other words, they are able to self-select and target specific tissues for which they are intended to act, while avoiding other tissues that typically lead to many side effects.

Several molecular mechanisms are responsible for the ability of ostarine to be “tissue-selective”, including [1]:

  • Conformation to the androgen receptor binding domain
  • Nongenomic signaling
  • Induction of gene regulation

It May Increase Muscle Mass

In its first preclinical studies, ostarine showed great capabilities to significantly increase muscle mass with only limited effects on other tissues [2].

In fact the power of ostarine was so evident that it appeared to improve muscle mass and strength without a supporting training program (I bet that got your attention!).

When ostarine began to be studied in humans, it continued to have good effects, with increases in lean body mass and physical function in healthy elderly men and cancer patients in comparison to placebo [3] [4] [5].

In terms of the extent of benefit, a clinical trial on nearly 100 postmenopausal women found that 3mg of ostarine for 3 months was able to increase lean body mass by ~1.5kg and significantly increase physical functioning, such as the strength of leg muscles [6].

It May Improve Bone Health

In addition, although most of ostarines physiological effects surround muscle metabolism, it also has vast osteoanabolic effects on bone tissue and thus improves bone density, strength, and structure.

This is as a result of ostarines antiresorptive (osteoclast inhibition) and anabolic (osteoblast differentiation) effects of [7].

However, the research on this area of ostarine is very limited and a clear connection cannot yet be made.

How MK-2866 Take?

In clinical trials, ostarine is being given to patients at 1-3mg per day with good results.

However, those buying ostarine on the black market are taking it at much higher doses of 10-25mg a day for 4-8 weeks.

More dramatic results seem to occur from these higher dosages, based on user reviews, however the risk of side effects also appear to greatly increase.

Ostarine can be taken in capsule or liquid form, with no evidence to suggest one method of use if superior to another (albeit pharmaceutical grade ostarine is always in liquid form).

MK-2866 Safety And Side Effects

In preclinical and clinical trials, ostarine appears to be generally safe and well tolerated at the dosages tested – up to 3mg per day.

Phase 2 clinical trials even began to show some potential health improvements while taking the drug, such as improvements in insulin sensitivity and reduced cholesterol levels [8].

In addition, unlike anabolic steroids, ostarine does not appear to negatively affect free testosterone, luteinising hormone, follicle-stimulating hormone, or estrogen levels in men [9], and does not trigger changes in hair growth or loss [10].

This being said, one study did find that ~25-35% of people taking 1-3mg of ostarine suffered from serious adverse events that required admission to hospital, and ~10% of these people had life-threatening adverse events [11].

Clearly this highlights a cause for concern and despite most studies finding no issues with safety, data such as this should still be a reason to avoid taking ostarine until more human research has been conducted and thoroughly analyzed.

Along with this, it seems as though most people experimenting with ostarine are taking far higher dosages than what has been studied. It goes without saying that safety cannot be guaranteed at doses that have not yet been tested. Anecdotal evidence of peoples bloodwork before and after using ostarine at these high doses indicates that it can significantly lower testosterone levels.

Not to mention that these same people are using ostarine products that are sourced online from non-pharmaceutical grade labs where potential contamination with unknown ingredients is very possible. A supplement company called Dynamic Technical Formulations have already been forced to recall their ostarine products because they were found to contain dangerous ingredients.

As a final note, although some claims flooding online suggest ostarine may be an “anti-cancer drug”, it has actually failed multiple phase 3 clinical trials to treat those with lung cancer [12].

Is MK-2866 Legal?

Ostarine is not currently approved for human use or consumption in any country.

This has led to many non-pharmaceutical companies creating their own ostarine products and marketing them to the general public, where safety cannot be guaranteed.

World anti-doping organizations also clearly state that ostarine is not allowed to be taken by athletes who are part of drug tested sports. Despite this, multiple cases of high-level athletes have been caught taking ostarine and have received large fines and bans from competing in future athletic events.


Ostarine is an androgenic drug that is advertised to produce steroid-like results without the side effects.

The current evidence suggests that it can increase lean body mass and strength at doses of 1-3mg per day without serious side effects, however most people are seemingly taking doses far beyond this.

At such high doses, safety cannot be guaranteed as the research is still in its early stages. More long-term research is also needed to prove its efficacy over time.

The drug is also not currently recommended for human consumption by food and drug administrations.

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