Ostarine (MK-2866): Before and After Pictures, Side Effects & Dosage

Dr George TouliatosDisclaimer: SARMs are only to be used for research purposes, as they are non-FDA-approved compounds and thus may cause adverse effects. If you have any questions or concerns, Dr. Touliatos is currently available for consultation.

Ostarine is a second-generation SARM (selective androgen receptor modulator), also known as Enobosarm or MK-2866.

Ostarine was formulated to mimic the anabolic effects of steroids but without the harsh side effects, thus theoretically providing a safer medication. The objective is for SARMs to improve the efficacy of treatment in patients suffering from cachexia, osteoporosis, and anemia.

Ostarine (MK-2866) was first described in 2001 and developed by GTX, Inc., a US biotechnology firm. Since then, it has been evaluated in phase I, II, and III clinical trials.

In two phase III trials, GTx announced that Ostarine was unsuccessful in the treatment of breast cancer patients suffering from cachexia. This was due to insignificant improvements in muscular strength, despite increases in muscle hypertrophy (size).

This has led to the biotechnology company ceasing its pursuit of ostarine for the treatment of cachexia but instead remaining committed to modifying MK-2866 for improved success in the future.

Due to Ostarine’s recent creation, it is not approved by the FDA for human use; thus, it is illegal to purchase for cosmetic purposes and is banned by sporting organizations such as WADA.

Ostarine and other SARMs are classified as ‘investigative compounds‘ and are only allowed for scientific research.

This has led to SARM manufacturers modifying their marketing strategy, labeling products as research chemicals instead of ‘dietary supplements, effectively taking advantage of this legal loophole or gray area.

Ostarine Benefits

Muscle Size and Strength

Ostarine mimics anabolic steroids’ anabolism by stimulating the AR (androgen receptor), increasing skeletal muscle and bone strength.

Ostarine also enhances satellite cell cycle activation, resulting in fusing with myofibres and increasing myonuclei in the muscles.

Due to ostarine’s tissue-selective properties, it can increase lean muscle without inducing the androgenic side effects of steroids, preventing benign prostatic hyperplasia (BPH).

In one study on elderly men and women, participants increased their lean body mass by 3% after taking 3 mg/day of ostarine for 12 weeks (1). This is the equivalent of an 80kg (176lb) man gaining 2.4kg (5.3 lb) of muscle.

These results are encouraging considering the dosage used (3 mg/day) is only a fraction of what weightlifters administer to improve their body composition.

These elderly men and women also experienced significant increases in muscular strength, adding 22 pounds to their bench press by the end of the 12 weeks.

No Virilization in Women

Women are particularly vulnerable to virilization effects when taking steroidal compounds. However, we have found ostarine to be very safe in this regard. Elderly women in the above-cited study also experienced no masculinization effects.

Fat Loss

Ostarine is an effective SARM for cutting due to its ability to improve insulin sensitivity and thus induce subcutaneous and visceral fat loss.

Reductions in visceral fat are a unique attribute of ostarine, in contrast to many anabolic steroids, which can increase VF.

This is why some steroid users have a protruding appearance to their waistline, indicative of high visceral fat levels.

However, on ostarine, you will notice fat loss all over the body, particularly in the midsection, reducing overall waist size.

Ostarine also has positive metabolic effects, increasing calorie expenditure throughout the day and improving the chances of users eating in a calorie deficit. Thus, it has direct and indirect lipolytic effects.

In the elderly study, users experienced a 0.6kg (1.3 lb) reduction in fat mass. We have seen more pronounced fat loss in non-elderly people on ostarine due to their combining it with regular weightlifting and cardiovascular exercise. In contrast, the elderly patients were sedentary.

Disclosure: We do not accept any form of advertising on Inside Bodybuilding. We monetize our practice via doctor consultations and carefully chosen supplement recommendations, which have given our patients excellent results.

Best Ostarine Source


Sports Technology Labs is our #1 rated source for Ostarine, due to them consistently formulating products at >98% purity; which can be authenticated via independent COAs (certificates of analysis).

Discount code: Save 15% on Ostarine and other SARMs by using discount code inside15.

Ostarine Side Effects

Ostarine does not appear to cause hypertrophy of the prostate; however, it does reproduce several steroid side effects (detailed below).

Testosterone Suppression

In the elderly study cited, the men taking 3 g/day of ostarine for 12 weeks experienced minimal fluctuations in serum testosterone levels.

Some of our patients utilizing higher dosages of ostarine have reported normal libido, nocturnal erections, and testicular size when taking 25 mg/day for 6 weeks (2).

However, our SHBG tests indicate that ostarine can cause low testosterone levels post-cycle. One user scored 148 ng/dL, compared to an average score of 264–916 ng/dL (for his age range). This was following 20 mg/day of ostarine for 8 weeks (3).

Thus, based on existing research and our anecdotal evidence, it is reasonable to conclude that ostarine has no significant effect on endogenous testosterone levels when taken in very small dosages.

However, in higher dosages, it can have a significant suppressing effect, which may not always be obvious to users (unless being tested) and may depend on how the compound affects the individual (potentially differing on a case-to-case basis).

Liver Toxicity

In the elderly study, AST/ALT liver markers increased above normal levels in 20% of participants, indicating ostarine’s hepatotoxic potential. Although levels did not rise to exceedingly dangerous levels, it is worth noting that such participants only took a fraction of the dose compared to gym-goers taking ostarine for physique-enhancing purposes.

Ostarine’s liver toxicity may be due to it being administered orally (swallowed via the mouth) and thus having to bypass the liver before becoming fully active, increasing stress and inflammation in this organ.

We have found that other SARMs, such as LGD-4033 (ligandrol) and RAD-140 (testolone), also have the potential to cause hepatocellular-cholestatic liver injury (4).

Cholesterol Issues

HDL cholesterol (the good type) was reduced by 27% when taking 3 mg/day of ostarine for 12 weeks. This is alarming, considering the tiny dosage used in this study; thus, ostarine has the potential to increase myocardial infarction (heart attack) risk in the short or long term, even in modest doses.

Ostarine and other SARMs’ ability to skew HDL/LDL cholesterol levels may be attributed to their oral nature, thus stimulating hepatic lipase in the liver upon entry, an enzyme known for decreasing HDL and increasing arterial plaque.

Gynecomastia and Water Retention

Some SARMs can elevate estrogen indirectly by binding strongly to the androgen receptor, leaving more natural testosterone available to convert to estrogen.

Consequently, some of our patients have complained of bloating or gynecomastia when using SARMs, despite a lack of the aromatase enzyme present.

However, ostarine users often report minimal water retention but instead a dry-looking physique. Improved insulin sensitivity also indicates ostarine’s minimal effect on this female sex hormone; thus, the risks of developing gynecomastia are thought to be low.

One user confirmed this by testing his estradiol levels post-ostarine cycle (5); they measured at a normal level, being 17.4 pg/mL (average range: 7.6-42.6 pg/mL). 

Hair Loss

Some of our patients report hair loss or recession during their cycle (6), despite the 5-alpha reductase enzyme failing to be present in ostarine and other SARMs.

The reason hair loss occurs is due to elevated DHT (dihydrotestosterone) levels, which are raised indirectly. When ostarine competes with your natural testosterone levels for binding to the androgen receptor, ostarine wins, leaving higher amounts of free testosterone to convert to DHT.

Although incidents of hair loss are not as rife compared to anabolic steroids, androgenic alopecia is still possible on ostarine (and other SARMs). 

Ostarine Results (Before and After Pictures)

ostarine before and after

This user’s results are after taking 20 mg/day of ostarine for 45 days in combination with regular weight training.

This user lost 3kg (7 lbs) in weight yet looks considerably more muscular due to greater levels of muscle definition. Thus, the scales may not be an accurate indicator of results when taking ostarine due to simultaneous muscle-building and fat loss. Before and after pictures are therefore a must when monitoring progress before and after cycles.

Note: In our experience, these results are above average. This user mentioned he had been training more regularly on ostarine, thus contributing to some of the muscle gain and fat loss.

Legal Ostarine Alternative


OSTA 2866 is our #1 rated legal Ostarine product. It replicates the fat-burning effects and muscle-building effects of Ostarine, but without any unwanted side effects.

It is FDA-approved and can be purchased online without a prescription.

OSTA 2866 is best suited for weightlifters wanting to reduce their body fat percentage, increase muscle definition and simultaneously add lean muscle tissue.

Ostarine Before and After #2

ostarine before and after

This user lost 13 pounds after cycling on ostarine for 6 weeks. He administered 12.5 mg/day during week 1, then 25 mg/day for the remaining 5 weeks.

He reported zero side effects, at least to his knowledge, but experienced a notable amount of fat loss, accompanied by increases in muscle fullness and vascularity.

Note: Eating in a calorie deficit may have aided in some of the fat burning during this transformation.

He believes ostarine did not help him build any lean muscle mass; however, it may have contributed to muscle retention during his cut. His strength levels remained exactly the same during his 6-week cycle.

Ostarine Before and After #3

ostarine before and after 3

The above user lost 23 pounds after an 8-week ostarine cycle, administering 20 mg/day.

He adopted a calorie-deficit diet during his cycle, contributing to substantial fat loss. He does not appear to have built any noticeable muscle mass, despite vast improvements in muscle definition.

He reports his strength staying the same, but credits ostarine for preserving his size and strength while cutting on low calories (1800 calories/day).

In terms of side effects, he monitored his liver enzymes and testosterone post-cycle. His ALT liver enzyme score was high, at 57 IU/L (approximately 30% over maximum average levels).

His testosterone levels were also low, despite being clinically diagnosed with hypogonadism and being eligible for prescribed testosterone replacement therapy. He also reported a crash post-cycle, feeling tired, and having low well-being, despite not feeling a ‘high’ on-cycle.

We have found ostarine results to be comparable to a mild anavar or winstrol cycle, with muscle gain and fat loss occurring synergistically and also with similar side effects.

Ostarine Dosage

ostarine sarmsDue to a lack of FDA approval, dosage guidelines have not been established for ostarine. However, in clinical studies, 3mg, 9mg and 18 mg/day have been utilized with some success.

Those taking ostarine to enhance their body composition commonly take 10–30 mg/day.

Women often take the lower value of this range, such as 10 mg/day, in a bid to avoid virilization effects.

It is believed that higher dosages of ostarine may further promote muscle hypertrophy and thus be more effective as a lean bulking cycle, compared to lower dosages that predominantly enhance fat loss, thus being a cutting cycle.

However, we have seen higher dosages of ostarine also exacerbate side effects, particularly cholesterol and liver values.

Ostarine Cycle

A common ostarine-only cycle, tailored for fat loss and muscle retention:

  • 20mg/day of ostarine for 8 weeks

Note: The above cycle is commonly used by men. Women will typically administer 10 mg/day for 4–8 weeks.

In some instances, ostarine may be cycled for up to 12 weeks; however, this is only suitable if cholesterol, liver, and testosterone values have not excessively deteriorated from the first 8 weeks.

Ostarine can be cycled with other SARMs simultaneously; however, this is not advised due to further elevations of blood pressure and liver enzymes.

Ostarine and Cardarine Stack

Some users commonly stack ostarine (MK-2866) with cardarine (GW501516) for enhanced results when cutting, specifically for more prominent fat loss.

Cardarine is not a SARM but a PPARD (Peroxisome Proliferator-Activated Receptor Delta) receptor agonist and has a positive effect on insulin sensitivity and fatty acid oxidation, thus potentially helping to treat obesity in medicine.

Research has observed cardarine to significantly reduce fat mass, both in animal and human studies (7).

Ostarine/Cardarine Cycle

  • Ostarine: 20mg/day for 8 weeks
  • Cardarine: 20mg/day for 8 weeks

Our lipid profiles have shown cardarine to have cardioprotective properties, increasing HDL cholesterol levels (8), and thus potentially reducing spikes in blood pressure from ostarine.

However, Dr. Thomas O’Connor has observed hepatotoxic effects from cardarine based on his observation of patient labs in over 2,000 SARM users. He likens its adverse effects on the liver to taking 50 mg/day of anavar; thus, stacking it with ostarine is likely to exacerbate liver values.

Cardarine is classified as a research chemical, similar to SARMs, due to its recent creation.

Cardarine first appeared in scientific research in 2001; thus, its side effects are yet to be fully understood.

Our concern with cardarine is its carcinogenic risk (9), with long-term animal studies showing a strong correlation with its use and various cancers.

People in the fitness community have criticized such studies, stating that excessively high dosages were utilized; however, even the smallest dosage range proved to be carcinogenic. This includes a 5 mg/kg dose, which, when calculated across species, translates to a 65mg dose in an 80kg human.

This is somewhat similar to the dosages utilized by fitness men and women today. Consequently, cardarine’s safety is in doubt, and thus it was pulled from further development in medicine in 2009.

How to Take Ostarine

Ostarine typically comes as an oral solution, dosed at 25 mg/mL, and is taken by mouth.

Users can measure the dose with an eye dropper or syringe before placing it in the mouth.

Ostarine may also be taken sublingually, with the liquid being placed under the tongue for 10–15 seconds before swallowing. Such placement allows the liquid to come into contact with the mucus membrane, creating a more direct and fast entry into the bloodstream (10). 

This administration methodology also inhibits presystemic metabolism, increasing ostarine’s biological availability.

Ostarine is sometimes available in capsule form, with 10mg of ostarine typically being present in each tablet.

Ostarine PCT

Ostarine is considered a mild SARM, thus complete shutdown of the HPTA (hypothalamic-pituitary-testicular axis) is unlikely.

However, notable suppression of testosterone is to be expected, thus a PCT is an option for ostarine users, depending on their symptoms and how hypogonadal they are.

If a user finds out their testosterone levels are on the low side but their well-being, energy, testicular size, and libido are normal, they may not utilize a PCT.

In this case, we typically find it takes several weeks for their endogenous testosterone to return to previous levels.

If users are experiencing a crash in energy levels post-cycle and diminished sexual health, they may choose to run clomid post-cycle. Clomid is a mild medication in comparison to Nolvadex, which is typically used for more potent SARMs or anabolic steroids.

Clomid will accelerate the recovery of the HPTA, helping to shorten the timespan of low testosterone symptoms (11).

As a PCT, we typically prescribe clomid for 30 days, dosed at 25 mg/day.

A PCT for ostarine should begin 3–4 days after the last dose, with it having a half-life of 14–16 hours and thus being fully cleared out of the body by that point. The clearance time is 5.5 times the half-life.


ostarine bottle
Ostarine (MK-2866) possesses potent fat-burning properties due to its positive effects on insulin sensitivity and stimulation of the androgen receptor.

Lean muscle gains, however, are mild and should be considered inferior to more potent SARMs, such as LGD-4033 or RAD-140.

The severity of SARMs’ side effects is often understated, and even mild SARMs (such as ostarine) present toxicity in relation to the heart and liver. Testosterone suppression is also likely to occur, leaving users temporarily hypogonadal.

In contrast, anavar, an oral steroid, may actually be safer than ostarine, with several decades worth of medical research documenting its effects. Anavar presents similar side effects to ostarine in regards to cholesterol alterations, raised liver enzymes, and testosterone suppression; however, these are often not problematic, hence anavar’s FDA-approved status in medicine.

Thus, we find anavar’s risk-to-reward ratio to be more desirable compared to ostarine, especially as it will yield greater results in terms of fat loss, strength, and muscle gains.

Co Authors :