Ostarine is a popular SARM used by bodybuilders to increase lean muscle mass and strength. It is also currently being researched for reversing muscle breakdown in muscle-wasting diseases. We review its potential uses and gains along with side effects, risks, and dosage based on the science and user reviews to give you up-to-date unbiased information about this drug.
Note: By writing this post, we are not recommending this drug. Some of our readers requested that we commission a post on it, and we are simply providing information that is available in the scientific literature. Please discuss your medications with your doctor. Ostarine is specifically a drug that we at SelfHacked would recommend against.
What Is Ostarine?
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 [R].
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. Due to their favorable safety and “cleaner” gains, SARMs have surfaced as a popular new class of appearance and performance enhancers [R].
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 [R, R].
Ostarine and other SARMs are being researched for their ability to improve serious muscle wasting diseases. Ostarine was initially developed to target muscle wasting diseases and prevent complete muscle loss. Interestingly enough, it is one of the few SARMs still in clinical trials (by GTx) while most others proved to be too toxic [R].
Ostarine may be approved for clinical use in the future if the ongoing clinical trials attest to its favorable benefits/risks ratio. However, its use in professional sports will almost certainly remain illegal. As things currently stand, 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.
- 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 or consumption in any country
- Long-term risks are unknown
Mechanism of Action
It’s no secret that androgens increase skeletal muscle mass — that’s the main physiological reason why men typically have more muscles than women. Being the main male sex hormones, the activity of androgens in the body go well beyond muscle-building. When sensors for androgens are non-selectively stimulated by drugs like steroids, the result is usually 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. Scientists are still trying to understand why in the hopes of uncovering newer and even more effective muscle-selective drugs.
Animal studies shed some light on exactly what Ostarine does in the muscles. 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) [R].
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 successful recovery from muscle injuries [R].
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 (double-blind randomized controlled trial), 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 [R].
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 [R].
Large clinical trials of enobosarm for preventing muscle loss in cancer patients are currently underway [R].
In rats, oral enobosarm was quickly and completely absorbed. It could be widely distributed throughout the body and eliminated via detox pathways [R].
2) Bone Health
A decrease in bone-protective sex hormones with age increases the risk of poor bone health and osteoporosis. While enhancing bone mineralization is important, increasing muscle mass can reduce the risk of bone fractures and speed recovery. Muscles support the whole skeletal system and their strength and good health aid in healing fractures, especially in older people [R, R].
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, though [R, R].
3) Heart Health
Ostarine may also prove to be beneficial for people with heart disease, who often suffer from muscle wasting and weight loss [R].
In a clinical trial of 120 healthy elderly people (double-blind randomized controlled trial), enobosarm (1-3 mg/day) lowered lipids in the blood such as triglycerides, total cholesterol, and HDL cholesterol. Healthy lipid levels help prevent heart disease. However, lowering HDL is not typically considered beneficial [R+].
4) Insulin Resistance
In the same above-mentioned study of 120 healthy elderly people (double-blind randomized controlled trial), enobosarm improved insulin resistance and lowered blood glucose. The effects were similar to standard anti-diabetic drugs such as metformin. Ostarine may benefit people with diabetes or metabolic syndrome with more research [R+].
Advanced Ostarine Research
- Ostarine has good bioavailability. Rats completely absorbed Ostarine, transported it throughout the body, and eliminated it via feces mostly as an unchanged drug [R].
- Dosage in clinical studies: Ostarine 1 mg/day increased total lean body mass by more than 3 pounds, while 3 mg/day increased it by only 2 pounds after almost 3 months in cancer patients. Elderly people gained muscle mass only on 3 mg/day [R, R].
- Ostarine and other SARMs are also being researched for potentially helping those with breast cancer, incontinence, low testosterone in older men, and muscular dystrophy (such as Duchenne Muscular Dystrophy) [R, R].
How Ostarine Is Used & Reviews
The official published 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.
Having in mind the higher doses and different goals of the bodybuilding community, 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.
One bodybuilder compared the results of Ostarine to low doses of steroids like EQ (Equipoise), Primo (Primobolan) or Anavar (Oxandrolone). Although its gains don’t seem to be 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. Because for many bodybuilders, few things are worse than losing all the muscle mass gained through sweat and hard work shortly after a cycle.
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 they say it doesn’t cause male-like hair growth, deepening of the voice, or other signs of high androgens.
- Pure, clean, dry lean muscle gains
- Milder gains than with steroids
- Increased protein synthesis
- Increased strength, stamina, and lifting endurance
- No water retention
- The lean keepable gains are ~6-8 lbs
- 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
- Combining Ostarine with PCT at doses above 30 mg/day
- 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.
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)
Some bodybuilders are completely against the concept of body recomposition, taking the stance that you should just choose: bulking or cutting.
For others, body recomposition is a good middle ground solution. They do it to increase muscle mass and burn fats while being on an almost eucaloric diet where calories consumed = calories expended. To be precise, the calories should be just a tad above this maintenance amount. Of the total calories, some say that ⅓ should come from lean proteins.
- Enhanced muscle recovery (at lower doses)
- Effects noticeable 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 to it.
As an Alternative
Some use Ostarine as an alternative to HGH and steroids.
Since the dosing data in clinical trials is limited, the Ostarine-community seems to have established unofficial dosing 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. Some report taking up to 37 mg/day, although this is usually not recommended. High doses are used by some men with approximately 200 lbs. 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 dose in men 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.
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 only 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.
Ostarine Side Effects and Cautions
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) [R, R].
Side effects from clinical studies include headaches and back pain. The long-term effects of Ostarine are unknown [R].
Ostarine has become extremely popular. Many professional athletes seek its muscle-building and endurance-enhancing benefits. Anti-doping agencies are well-aware of this and are always developing new ways to screen for SARMs like Ostarine in the urine. More precise screening tests make it hard for any professional athlete to get away with using Ostarine [R, R].
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.
The side effects users reported include the following:
- No increases in muscle size or strength after 5 weeks
- 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
- Increased estrogens with high doses
- Menstrual cycle imbalances
- Acne and skin changes with higher doses
- Although uncommon, some users do report gyno flare ups. One side of the nipple can become slightly enlarged and painful. Sometimes both nipples are affected.
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 (inhibitor like 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.
A couple of users mentioned increased hunger while taking Ostarine — desirable during bulking but not so much in cutting cycles.
Some women reported missing their period while on Ostarine. Menstrual cycles usually returned back to normal after stopping it.
Although Ostarine is available online as a research chemical, we at SelfHacked advise against using this drug given that its long term safety has not been confirmed in humans.