Ostarine is a SARM used to increase lean muscle mass. It is also currently being researched for reversing muscle breakdown in muscle-wasting diseases. Learn Enobosarm’s potential uses, benefits, side effects, dosage & where to buy.

Disclaimer: By writing this post, we are not recommending this drug. 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.

What Is Ostarine?

Steroid or Not?

Ostarine (MK-2866), also known as enobosarm, is a selective androgen receptor modulator (SARM). SARMs like Ostarine stimulate steroid hormone receptors — androgen receptors — mimicking testosterone [1].

Unlike typical steroids, though, SARMs can target specific tissues, such as the muscles or bones. This limits their side effects, which means that people who take SARMs don’t have to deal with severe testosterone suppression and increased estrogens [1].

Due to their favorable safety and “cleaner” gains, SARMs have surfaced as a popular new class of appearance and performance enhancers.

Many bodybuilders and athletes swear by Ostarine and claim it offers significant muscle mass and performance gains with few risks.

Based on its mechanism of action, Ostarine should be safer than steroids. Although it’s also potentially safer than other SARMs, it has not yet been approved for human use anywhere in the world [2, 3].

Ostarine is being researched for its ability to improve serious muscle wasting diseases. Interestingly enough, it is one of the few SARMs still in clinical trials while most others proved to be toxic. It may be approved for clinical use if the trials attest to its favorable benefits/risks ratio [3].

However, its use in professional sports will almost certainly remain illegal. The World Anti-Doping Agency banned Ostarine under the S1 Anabolic Agent category of the Prohibited List, along with all other SARMs back in 2008.

Ostarine is a selective androgen receptor modulator (SARM) touted to safely boost muscle growth. Although banned in professional sports, it’s still being medically researched.



  • Increases lean muscle mass and strength
  • Shouldn’t cause hormonal imbalance
  • May improve bone strength
  • May lower cholesterol and improve insulin resistance
  • Only mild side effects have been reported


  • Not allowed for use in professional sports
  • Not approved for human use
  • Long-term risks are unknown

Mechanism of Action

It’s no secret that androgens increase skeletal muscle mass — that’s the main reason why men typically have more muscles than women. The activity of androgens in the body go well beyond muscle-building, though. When sensors for androgens are non-selectively stimulated by drugs like steroids, it usually results in a long list of side effects.

SARMs specifically target muscles and increase anabolic processes while sparing the reproductive organs. Among many synthesized SARMs, the structure of Ostarine seems to offer some advantages.

In one study on mice, Ostarine was as effective as the most influential androgen, dihydrotestosterone, at restoring the size of pelvic floor muscles. Muscles in the pelvic floor are especially rich in androgen receptors (AR) [4].

Ostarine could also activate muscle stem cells (satellite cells), which help remodel and regenerate muscles. Surprisingly, it turned out that Ostarine also stimulates cells in the connective tissue, which are important for a successful recovery from muscle injuries [4].

Ostarine increased the activity of the insulin-like growth factor 1 gene (IGF-1), which boosts muscle growth and strength [4, 5].

Ostarine targets specific androgen receptors in muscles to cause anabolic effects while sparing reproductive organs. It helps build and regenerate muscles and connective tissue.

Potential Uses of Ostarine

This section focuses on the clinical and scientific research that backs up the potential use of Ostarine for muscle-wasting diseases. If you’re just interested in the bodybuilding aspect and reviews, skip to this part of the article.

1) Muscle Mass

Ostarine is being researched for reversing muscle loss in cancer patients, people with muscular dystrophy, and the aging population.

In a clinical trial of 120 healthy elderly people, enobosarm increased lean muscle mass and fitness. Only those who received 3 mg of enobosarm daily for 12 weeks saw benefits, while lower doses did not work as well. Importantly, its side effects were similar to placebo, with no steroid-like risks [6].

In another trial, enobosarm safely increased lean muscle mass in 159 cancer patients. Cancer patients who already started to lose muscle mass prior to the study gained about 2 – 3 lbs after taking enobosarm for about 4 months. The lower (1 mg/day) and the higher (3 mg/day) dose worked equally well [7].

Large clinical trials of enobosarm for preventing muscle loss in cancer patients are currently underway [8].

Ostarine may increase muscle mass and prevent muscle wasting in older people and cancer patients without causing steroid-like side effects.

2) Bone Health

A decrease in bone-protective sex hormones with age increases the risk of poor bone health and osteoporosis. Increasing muscle mass can reduce the risk of bone fractures and speed up recovery, especially in older people [9, 10].

Since Ostarine mimics testosterone in the muscles and bones, it has the potential to prevent bone diseases. Animal studies confirmed that SARMs like Ostarine could increase both muscle and bone strength. No human study has confirmed the benefits yet [9, 3].

3) Heart Health

Ostarine may also be beneficial for people with heart disease, who often suffer from muscle wasting and weight loss [11].

In a clinical trial of 120 healthy elderly people, enobosarm (1-3 mg/day) lowered triglycerides, total cholesterol, and HDL cholesterol. Healthy lipid levels help prevent heart disease. However, lowering HDL is not typically considered beneficial [12].

4) Insulin Resistance

In the above-mentioned study, enobosarm improved insulin resistance and lowered blood glucose. The effects were similar to standard anti-diabetic drugs such as metformin. With more research, Ostarine may benefit people with diabetes or metabolic syndrome [12].

According to limited clinical evidence, Ostarine may lower blood lipids and sugar and improve bone health.

Advanced Ostarine Research and Dosage

Ostarine has good bioavailability. Rats completely absorbed Ostarine, transported it throughout the body, and eliminated it via feces mostly as an unchanged drug [13].

Dosage in clinical studies: 1-3 mg/day, up to 4 months [14, 6].

Ostarine and other SARMs are also being researched for breast cancer, incontinence, low testosterone in older men, and muscular dystrophy [3, 15].

How Ostarine Is Used & Reviews

The official scientific research about Ostarine tells us very little about its real-world use and what to expect when taking it for bodybuilding. It was researched only in cancer patients and elderly people. To bridge the gap, here we summarized the vast amount of available reviews and feedback from online communities with the attempt of teasing apart the most useful information.

Note: All the information below is anecdotal and based on only on personal experiences of Ostarine users. We can’t attest to its accuracy. We also can’t say to what extent these experiences are affected by other SARMs or different drugs/supplements taken at the same time. And lastly, we are far from sure about the actual content and quality of Ostarine in numerous products users bought online.

Bodybuilding Benefits

The reported benefits of Ostarine appear like an enlarged, exaggerated image of the effects reported in clinical trials. For example, cancer patients gained 2 – 3 lbs after taking 3 mg/day for 4 months, while bodybuilders report gaining 6 – 8 lbs from approximately 25 mg/day during bulking cycles.

Ostarine is seen as hard to rival among most people who have used it. Bodybuilders swear by its safety and dry muscle gains. It’s even being called the “most well-rounded SARM”.

Based on the bodybuilding reviews, Ostarine offers all the benefits of steroid drugs without the nasty side effects. Most users consider it a clean drug since it helps them increase pure muscle mass and burn fat with minimal side effects.

Although its gains aren’t too dramatic, the gains/risks profile seems to be superior most other SARMs and bodybuilding drugs or supplements.

Those who do use steroids take Ostarine as a PCT or in between cycles of steroids to maintain muscle gains. Others who stick to SARMs still take regular PCT after Ostarine cycles.

Additionally, users claim the results gained with Ostarine are easier to maintain. This may be even more important than its more apparent muscle-bulking effects. All in all, bodybuilders claim it offers gains in all phases – from bulking cycles and cutting to body recomposition and muscle recovery.

Women seem to prefer Ostarine as well, since it supposedly doesn’t cause male-like hair growth, deepening of the voice, or other signs of high androgens.

Ostarine is favorite among bodybuilders for lasting dry muscle gains and excellent safety. They cycle it instead of typical steroids or use it between the cycles.

Bulking Cycles

Users report:

  • Pure, clean, dry lean muscle gains (~6 – 8 lbs)
  • Milder gains than with steroids
  • Increased strength, stamina, and lifting endurance
  • No water retention
  • Great pumps during workouts
  • Increased energy and sense of well-being
  • No post-cycle crashes
  • No need for pre-cycle supplements
  • No need for liver-support supplements
  • No increases in aggression
  • Women report more obvious muscle gains and fat loss than men

Cutting & Fat Burning

Users report the following effects of Ostarine for cutting cycles:

  • The Big One: maintaining muscle mass
  • No strength loss
  • Fat loss

For all bodybuilders, the major downside to cutting cycles is muscle loss. That’s probably why so many love Ostarine – they say it prevents muscle breakdown but helps burn fat. This is probably the most talked-about benefit of Ostarine for bodybuilding and where this drug seems to be unique.

Going back to the basics, it’s impossible to avoid being in caloric deficit if you want to burn fat and lose weight. However, your body will always interpret caloric deficit as a signal to break down all available energy stored in the body, including the proteins in your muscles.

Users report that Ostarine stalls this catabolic process, apparently stopping the body from using proteins as fuel but still helping to burn fats. It helped users maintain muscles despite being on a low-calorie diet, keeping the anabolic processes going. Ostarine is sometimes combined with Cardarine to boost cardio endurance.

Having in mind that Ostarine can prevent muscle loss even in life-threatening diseases (like in cancer patients) and in minimally active older people, it makes sense to think it could do the same in healthy people on a cutting diet.

Ostarine is popular in bulking cycles but even more so in cutting cycles. Users swear by its ability to stimulate fat burning while preventing muscle loss.

Body Recomposition

Used for re-comping, Ostarine users reported:

  • Gaining muscles
  • Losing fat
  • Gaining some weight overall (depending on the diet and total number of calories consumed per day)


Users report:

  • Enhanced muscle recovery (at lower doses) after a week or two
  • Improved injury prevention
  • Better joint mobility
  • Healing of bone and tendon injuries

Coming off TRT

One user explained how taking only Ostarine allowed him to maintain muscle gains after coming off TRT (testosterone replacement therapy). He didn’t lose any weight and even reported increased strength. A rebound effect after TRT is common and muscle loss is one of the most feared downsides.

Bodybuidlers report great results with Ostarine for recovery, injury prevention, body recomposition, and coming off typical steroids.

Bodybuilding Dosage

Since the dosing data in clinical trials is limited, the Ostarine-community seems to have established unofficial dosage guidelines based on trial and error.

Bulking doses (3 – 8 weeks):

  • Most male bodybuilders use 25 mg/day
  • Women typically use up to 10 mg/day

The dose favored by most men for bulking is almost 10 times greater than the dose used in cancer patients. Since Ostarine has a long half-life (24 h), most people take the daily amount all in one shot. Some still split the daily dose into 2-3 chunks.

Cutting doses (4 – 8 weeks) or for injury prevention:

  • Men: 15 – 20 mg/day
  • Women: not mentioned, but the men dose is usually halved

Body recomposition (4-8 weeks)

  • The dose ranges between 12.5 – 25 mg/day

Some users reported taking Ostarine alone (especially for bulking cycles) while others combine it with other SARMs and slightly lower its dose.

The usual bulking dosage for men is 25 mg/day (4-8 weeks), while the doses for cutting and recomposition range between 12.5-25 mg/day. Women typically take two times less.

Cycles & Time Off

Ostarine is commonly cycled for up to 12 weeks. Users who stopped cycles at the 8-week mark experienced fewer side effects. While some users don’t experience any side effects even with cycles lasting over 12 weeks, the chances undoubtedly increase.

As a general rule among experienced bodybuilders, time off should equal the duration of the cycle. As an example, this would mean taking a 12-week break from ostarine after cycling it for 12 weeks and using PCT for 3-4 weeks. The time off is usually counted after PCT.

Some think that the strict time on=time off rule should be abandoned for more personalized strategies. Proponents of shortening the time off recommend ordering detailed lab tests after the cycle + PCT to assess overall hormone levels and any potential problems.

If everything is alright, some restart Ostarine cycles soon after (1-week breaks). However, if the labs point to health problems, delaying Ostarine or any other bodybuilding supplements is a must for all sensible users.

Most bodybuilders use Ostarine in cycles of 8-12 weeks, followed by equal time-off. Shorter cycles may reduce the risk of side effects while shorter breaks increase it.


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We at SelfHacked advise speaking to a doctor before taking any drug, especially an unscheduled drug with limited long-term safety data in humans.

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Ostarine Side Effects and Cautions

Clinical Data

As mentioned, the World Anti-Doping Agency banned SARMs as they can increase physical fitness and stamina.

In clinical studies, Ostarine was well tolerated and posed an insignificant risk of drug interactions with commonly used medication (antibiotics, antifungals, statins, and Celebrex) [16, 17].

Side effects from clinical studies include headaches and back pain. The long-term effects of Ostarine are unknown [18].

Beyond the Clinical Data

The truth is that so little information is out there about the side effects of Ostarine. Being a banned substance with clinical research done only in cancer patients, the available scientific literature doesn’t offer much useful information.

To get a better idea of what side effects Ostarine may or may not cause, we decided to take a closer look at its structure and user reviews.

As a non-hormonal SARM, Ostarine won’t be metabolized into steroid hormones in the body. It shouldn’t raise estrogen levels much. Steroids raise female sex hormones and can lead to annoying side effects like gynecomastia, enlarged breast tissue in men. Likewise, Ostarine shouldn’t affect the prostate, sexual, or vital organs.

Although Ostarine shouldn’t cause a full-blown hormonal imbalance, it has been reported to raise blood estradiol to an extent. Based reports we came across so far, the increase is very mild.

Unlike steroids, Ostarine shouldn’t cause water retention or trigger dramatic drops in testosterone production. Slight testosterone suppression is still possible and seems to be more likely at higher Ostarine doses.

Unlike typical steroids, Ostarine use bears a much lower risk of elevated estrogen and suppressed testosterone. These are still possible, especially at higher doses.

User Reports

The side effects users reported include the following:

  • Decreased sense of wellness after the first 9 days
  • Testicle Pain
  • Joint pain
  • Reduced strength
  • Testosterone suppression 4 weeks after stopping it (didn’t do PCT)
  • Erection difficulties
  • Disrupted sleep
  • Low energy
  • Depression
  • Increased estrogens with high doses
  • Menstrual cycle imbalances
  • Acne and skin changes with higher doses
  • Headaches
  • Increased hunger
  • Nausea
  • Baldness
  • Although uncommon, some users do report gyno flare-ups

Again, it’s unknown if some of the users also took steroids, other drugs, or what the Ostarine content in their product was.


With the goal of minimizing estrogens and the detrimental effects on testosterone short- and long-term, most bodybuilders start PCT right after an Ostarine cycle. PCT (Post-Cycle Therapy) consists of anti-estrogens (like Clomid, Nolvadex), which are usually taken for 3-4 weeks.

Users who are more sensitive to estrogen or those using high doses (35 mg/day) combine it with aromatase inhibitors (Anastrozole/Arimidex), which prevent the conversion of androgens to estrogen.

The opinions are mixed when it comes to PCT. Some don’t feel the need for it after Ostarine, especially with lower doses (approximately 10 mg/day). Others consider both anti-estrogens and aromatase inhibitors a must after Ostarine cycles. Users who check their labs and see increased estrogens start aromatase inhibitors during a cycle.

For some users, PCT with anti-estrogens after each Ostarine cycle is a must, while others don’t do it. Some combine it with aromatase inhibitors to lower estrogen levels.

Ostarine is a selective androgen receptor modulator (SARM) that supposedly boosts muscle growth with a few side effects. It targets specific androgen receptors in muscles to cause anabolic effects while sparing reproductive organs. Officials have banned its use in professional sports.

Ostarine may increase muscle mass and prevent muscle wasting in older people and cancer patients without causing steroid-like side effects. According to limited clinical evidence, it may also improve blood lipids, sugar levels, and bone health.

Ostarine is favorite among bodybuilders for lasting dry muscle gains, fat loss, and excellent safety. They also report great results for recovery, injury prevention, and coming off typical steroids. The anecdotal bodybuilding dosage ranges between 12.5-25 mg/day, 10x more than used in clinical trials. Users cycle it for 8-12 weeks, with or without PCT.

Side effects from clinical studies include headaches and back pain. Bodybuilders have reported testosterone suppression, joint pain, mood issues, and more. Higher doses and longer cycles increase the risk of side effects and their severity.

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