Ostarine (MK-2866; Enobosarm): Dosage, Results, Side Effects & Reviews

Ostarine is the trademarked name for a Selective Androgen Receptor Modulator (SARM) that is not approved for human use or consumption in the U.S., or in any other country. In recent years, WADA has reported an increasing number of positive tests involving SARMs, and athletes who use these substances most likely obtain them through black market channels.

Research has shown that SARMs like ostarine have fewer androgenic properties, meaning they have less influence on the development and balance of male hormones, including testosterone.

While they are not yet approved for human use, SARMs are of interest to the medical community because they might be effective at treating different health conditions without resulting in the negative side effects of steroids. Ostarine is currently being investigated as a way to treat a variety of muscle wasting diseases, such as osteoporosis, cancer, and hypogonadism.

Is ostarine prohibited in sport?

Yes, ostarine is prohibited at all times under the S1 Anabolic Agent category of the WADA Prohibited List. The number of positive tests involving ostarine has increased steadily over the past few years, with WADA reporting 28 globally in 2015.


How It Works

Ostarine binds to the androgen receptors just like anabolic steroids do, but it does this selectively, which means that it has considerably less side effects.

Ostarine is the most well known and extensively studied selective androgen receptor modulator (SARM) right now.

It is categorized as a SARM because of its unique selectivity at the androgen receptor where it exhibits a significant amount of anabolic activity in the body relative to androgenic activity.

It is being researched to determine if it is a potential treatment for the management of muscle and bone wasting diseases.

Testosterone was the first anabolic androgen to be approved for use in a clinical setting,  however, its scope of versatility has always been severely limited by its androgenicity and its pharmacokinetic issues.

Most notable being its lack of selectivity for muscle tissue to other androgen affected tissues like the prostate, and not being orally bioavailable [R].

This lack of selectivity disqualifies Testosterone entirely in a clinical setting for treating women, as well as men in many scenarios, due to the significant androgenic activity that would occur at a systemic level during the attempted management of muscle or bone wasting diseases.

This is where SARMs like Ostarine display such promise as viable alternatives [R].

Luckily, ostarine is extremely mild and well tolerated by those who use it. It is very uncommon to experience side effects while on cycle. Out of all of the SARMs you can use, Ostarine has the least likelihood of causing any unwanted side effects.

Scientifically, multiple studies demonstrate its high safety profile and efficacy, making it the perfect choice for those who are concerned with potential side effects from sarms.

By exhibiting such a favorable selectivity for stimulating increases in muscle tissue and strength relative to androgenic activity in affected tissues, Ostarine has the potential advantage that it could be used at relatively low doses, is orally bioavailable, and could potentially circumvent some of the negative effects that stem from traditionally used anabolic Steroids converting to 5α-reduced androgens in modern medicine that may raise the risk of benign prostate hyperplasia, accelerate the development of prostate carcinoma, increase the probability of acne breakouts, and exacerbate/substantially expedite androgenic alopecia (male pattern baldness).

It could also potentially eliminate the incidence of androgenic side effects in women entirely, while still potentially inducing enough anabolic activity to offset any muscle or bone loss occurring from degenerative disease.

While this is beneficial for both men and woman, its lack of androgenicity in women makes this a very promising anabolic agent.

Even minor amounts of androgens can cause virilization, making it extremely difficult to find compounds potent enough to offset degenerative diseases with no side effects in women.

Not only does Ostarine increase muscle mass and strength, it increases tendon strength, ligament health, bone density and encourages collagen turn-over [RR].

It also has good oral bioavailability [R].


Healing Abilities

Another reason why ostarine is so popular among bodybuilders and powerlifters, is that it has some noticeable abilities to strengthen bones and joints. This is a very important trait, since athletes may run into such nagging injuries as forearm or shin splints, neck pain, joint pain, back pain and many other injuries that never seem to go away. Unfortunately, many athletes make the mistake of taking harmful drugs to dull or kill the pain, which is merely a band aid, and on the long run this kind of abuse will make the injury go chronic and permanent.

However, ostarine can work its magic by increasing tendon strength, ligament strength, and bone density at a dose under 20 milligrams (mg) per day. Moreover, it doesn’t merely cover up the problem – ostarine actually fixes it. Thus, athletes will love ostarine’s healing effects on their inflamed joints.

MK 2866 can be used to bulk, cut, and even recomp (lose fat while gaining muscle). It’s a staple in many sarms cycles for this very reason.

You can also stack it with other compounds to improve your overall results.

In my own experience, I’ve found that Ostarine works best on a cutting cycle, especially stacked with cardarine or andarine.


Side Effects

Ostarine is not liver toxic, and it will not cause blood pressure or other organ strain.

However, some users have reported gynecomastia build up when running high dosages for extended periods of time. Hence, having an AI (aromatase inhibitor) on hand could be a good idea.

As stated, ostabolic is non-suppressive when used for 4 weeks or less at proper dosages, so no PCT is necessary. Nevertheless, those who choose to run higher dosages, and for longer periods of time, should run a PCT.

Depression / Anxiety

I’ve only seen this happen in one case, and it may not be due to using SARMs. This user reported feeling depressed around a week after starting ostarine.

In my opinion, this could be caused by a slight dip in testosterone levels, or it could just be a placebo. Worth noting, nonetheless.

Hair Loss

Hair loss from sarms ONLY occurs in people who already have male pattern baldness. If your hairline is fine, this does not apply to you.

This user on the AnabolicMinds forum reported hair shedding on ostarine, but also mentioned in a later post that it reversed after stopping use.

I find is suspicious that it caused hair loss, since it is not androgenic in nature. It is very possible that this user received a fake product (that contained prohormones) and that is what caused the shedding.


Some people with naturally low testosterone might experience some lethargy while on cycle. This is because sarms slightly suppress your body’s natural production of testosterone.

The good news is that your body will naturally fix the imbalance within a month after you stop taking it. Studies show it takes around 5 weeks to completely recover.

Note: The above study was completed using LGD 4033

If you have been diagnosed with low T, you might want to consider getting on TRT prior to starting a cycle.

Decreased Good Cholesterol (HDL)

The clinical data on this is inconsistent as there are some studies that show reductions in serum lipids (namely HDL and LDL) occurring in a dose dependent manner with Ostarine usage, as well as data showing only reductions in HDL levels (otherwise known as “good cholesterol”) [RR].

We at least know for sure that Ostarine has a negative effect on HDL levels, which is notable as this is a common side effect of all traditional anabolic steroids, and other SARMs.

Despite SARMs ability to avoid significant androgenic activity in the body, they evidently do not differ much from anabolic steroids in their effects on lipid profiles.

Testosterone Suppression 

SARMs have shown to suppress luteinizing hormone (LH) and follicle stimulating hormone (FSH) through the hypothalamus-pituitary-testis axis, thus decreasing testosterone in a dose-dependent manner [R].

Ostarine has also shown to significantly lower Sex Hormone-Binding Globulin (SHBG) and serum total testosterone levels in clinical trials in subjects treated with 1 mg of Ostarine or higher [R].

While SHBG was always significantly impacted at notable dosages, suppression of LH and FSH wasn’t consistently proven throughout Ostarine’s clinical trials.

However, after referencing anecdotal logs of baseline pre-Ostarine blood work compared to mid-Ostarine blood work with dosages several times higher than the 0.1 mg, 0.3 mg, 1 mg, 3 mg dosages used in trials (users commonly use Ostarine at upwards of 25 mg per day for several months), I believe it’s safe to say that Ostarine does also show blatant reductions in all of these hormones markers in a dose dependent manner, the dosages in the studies just weren’t high enough to yield this data.

The degree to which even high dosages of Ostarine suppress LH and FSH is far less than that of traditional anabolic steroids though, which should be noted.

The process of recovering to baseline healthy endocrine function would be hindered to a far greater extent in steroid users.


What Results To Expect

Ostarine causes some incredible changes in your body when taken. I am going to mainly focus on the physical results since that’s what most of my readers care about.

If you’re interested in some of the other health benefits of sarms, you can refer to this study.

Muscle Growth

It’s not a secret that SARMs can help you build large amounts of muscle. Ostarine is no different. During an 8 week cycle of Ostarine, you can expect to gain around 7-10lbs of lean body mass.

This study shows that in addition to gaining a considerable amount of muscle mass, test subjects saw a nearly 30% reduction in insulin resistance. If you follow any of the research regarding intermittent fasting (sometimes called Lean Gains), you know that insulin sensitivity is a crucial part of how effectively your body can utilize carbs. According to the study:

…subjects treated with 3 mg/d of Ostarine had on average an 11% decline in fasting blood glucose, a 17% reduction in insulin levels, and a 27% reduction in insulin resistance (homeostasis model assessment) as compared to baseline…Narayanan R, Mohler ML, Bohl CE, Miller DD, Dalton JT. Selective androgen receptor modulators in preclinical and clinical development. Nucl Recept Signal. 2008;6:e010. doi:10.1621/nrs.06010

Bottom line? Ostarine stimulates muscle growth by targeting anabolic pathways and by reprogramming your body to more efficiently utilize carbs.

Fat Loss

Although not a direct aide to thermogenesis, Ostarine can help promote fat oxidation in humans:

Secondary endpoints included safety of GTx-024, effects on fat mass, bone mineral density, blood glucose, and insulin. This study is the first to demonstrate the ability of a nonsteroidal, orally bioavailable SARM to increase lean muscle mass and improve physical function.Dalton JT, Barnette KG, Bohl CE, et al. The selective androgen receptor modulator GTx-024 (enobosarm) improves lean body mass and physical function in healthy elderly men and postmenopausal women: results of a double-blind, placebo-controlled phase II trial. J Cachexia Sarcopenia Muscle. 2011;2(3):153-161. doi:10.1007/s13539-011-0034-6

Users who are in a caloric deficit will experience much better muscle retention compared to natural lifters. Don’t be afraid to push the envelope when it comes to cutting calories. If you’re on cycle, you can easily maintain your current muscle mass in a 1000 calorie deficit.

In addition, it has been proven that increasing muscle mass will increase TDEE (how many calories you need a day). When you gain muscle, your body will naturally burn more fat as energy in order to keep that muscle.

Strength Gains

Ostarine especially shines when combined with strength training, and users consistently report strength gains similar to those found in anabolic steroids.

In fact, it is not uncommon to add 30lbs or more to your one rep max for bench press or squats. Strength gains are one of the first things people tend to notice when they’re taking ostarine.

Having a stronger body will inevitably improve your athletic performance regardless of what sport you play (if any). I’ve talked to football players, sprinters, rowers, even basketball players. All of them reported positive increases in their performance during and after their cycles.



Ostarine has a half-life of 23.8 hours, making once per day dosing a viable option for maintaining stable blood serum concentrations [R].


Ostarine Bulking Cycle

In a calorie surplus Ostarine will promote more lean muscle gains than would otherwise be possible to gain naturally.

For use in a performance enhancing context, cycles like the following are commonplace among users.

MK-677 (Ibutamoren) and/or S4 are commonly stacked alongside Ostarine in more involving performance enhancement bulking protocols.


Ostarine Cutting Cycle

In a calorie deficit Ostarine will retain much more lean muscle mass than would otherwise be possible naturally.

For use in a performance enhancing context, cycles like the following are commonplace among users (the length of this may vary depending on the user’s individual timeline constraints for reaching a goal body fat percentage).

Cardarine (GW501516) and/or S4 are commonly stacked alongside Ostarine in more involving performance enhancement cutting protocols.


Ostarine PCT (Post Cycle Therapy)

Ostarine will suppress natural Testosterone levels (and overall endocrine function) in a dose dependent manner.

It is wise to complete a PCT phase (post-cycle therapy) after an Ostarine cycle.

Due to Ostarine’s half-life, PCT should be started the day after the last Ostarine dosage was taken.

Forgoing PCT will put one at risk of muscle loss, fat gain, among all of the other standard side effects associated with Testosterone suppression.

If you are dead set on using performance enhancing drugs shortly after Ostarine, I would not advise following the broscience derived “time on = time off” equation.

Time off should be dictated by a variety of more individual specific factors, and blood work.

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