Everything You Need To Know About Ostarine (MK 2866)

Bodybuilding showing results from Ostarine cycle

Ostarine is supposed to help you build muscle and burn fat without the side effects of steroids, but is it worth it?  Read on and find out…

When it comes to SARMs, Ostarine (MK 2866) is perhaps the most well-known and widely used.

But do you actually know what it is, how it works, or how safe it is?

Since much of the narrative surrounding SARMs in general is influenced by the companies that sell them, the muscle-building benefits of SARMs, especially Ostarine, have been hyped to no end and the potential risks have been completely ignored.

The pitch goes something like this…

Ostarine can help you pack on pounds of muscle while burning fat, just like steroids, but without causing any of the side effects associated with steroids!

Sounds great, but how accurate is it?

Well, that’s exactly what we’re going to get to the bottom of this article.

We’ll look beyond the hype, at the actual research behind Ostarine.  Once you know the whole story, you can decide for yourself if it’s worth taking.

Here’s the pure, unadulterated truth about Ostarine…

What Is Ostarine And How Does it Work?

ostarine capsules

Ostarine is the trademarked name for a synthetic drug which belongs to a class of similar drugs known as Selective Androgen Receptor Modulators, or SARMs.

It also goes by the names:

  • MK 2866
  • Enobosarm
  • GTx-024

Out of all the SARMs, Ostarine is the most popular choice for people who want to build muscle.

It was originally developed by the pharmaceutical company GTX as a drug to treat diseases characterized by muscle wasting and deteriorating bone health.

These days, however, Ostarine is used by people who want to build muscle and strength beyond what can be achieved naturally while also dodging many of the side effects of traditional steroids.

Ostarine works by selectively increasing androgenic (testosterone) activity in muscle and bone tissue.

Unlike steroids, which increase whole body androgenic activity, Ostarine doesn’t have much of an impact on androgen receptors in the prostate, liver, or brain.

That’s what separates SARMs like Ostarine from steroids.

SARMs selectively increase androgen activity in muscle and bone, while steroids increase androgen activity in all tissues.

Out of all the SARMs currently available, Ostarine has the most research behind it.

The Research On Ostarine

Ostarine is still in clinical trials and, compared to other SARMs, it is the further along.

In mice, it has been shown to increase skeletal muscle mass by directly increasing androgen receptor activity in muscle tissue, but unlike most SARMs, there have actually been some human studies as well…

Ostarine has also been shown to preserve muscle mass in cancer patients.

It has also been shown to increase muscle mass and enhance exercise performance in elderly (but healthy) men and woman.

In a double-blind, placebo controlled Phase II clinical trial, subjects consuming 3mg of Ostarine daily for 12 weeks gains experienced, on average, lean body mass increases of 2.8lbs (1.3kg) while losing 1.8lbs (0.6kg) of fat mass.

Ostarine also improved Insulin sensitivity and reduced HDL (bad) cholesterol.

Most SARMs have only been studied in mice.  Those that have been studied in humans have only been studied in humans with some sort of medical condition.

The only other SARM besides Ostarine which has been studied in healthy human subjects is Ligandrol.

Other than that, the benefits and safety profiles of these substances are based on studies in rodents.

What Kind Of Results Can You Expect From Ostarine?

man looking at his arm muscles

I’d like to first point out one simple fact…

Everything you’ve heard about the benefits of Ostarine is either derived from one of two human studies or someone’s anecedotal (subjective) experience with the drug.

In the eyes of science, it’s impossible to say just how much muscle you can build with Ostarine, or how close it is to certain steroid compounds.

It just hasn’t been studied enough yet.

Based on anecdotal reports, though, a 30 day cycle of Ostarine could result in high single-digit lean mass gains with a slight reduction in fat mass, similar to a weak dose of a not-so-powerful steroid.

Longer cycles (8-12) weeks may lead to low double-digit lean mass gains and more fat-loss.

Some people have pushed Ostarine to the extreme, taking more than 25mg for longer than 12 weeks, but it’s not clear that those types of cycles are necessarily better.

As with most muscle-building compounds, there probably a point of diminishing returns, beyond which more Ostarine doesn’t necessarily equal more gains and the side effects begin to outweigh the benefits.

Also, how you train and how you structure your diet will determine your results in the end.  Even with steroids, you need to train hard and eat right to make considerable progress.

Ostarine is no different in that respect.

Ostarine Dosage

The Phase II clinical trial I mentioned above, in which Ostarine was shown to increase muscle mass, decrease fat mass, and improve exercise performance, tested doses of:

  • .1mg
  • .3mg
  • 1mg
  • 3mg

1mg of Ostarine was effective but 3mg was more effective, indicating a dose-dependent relationship.

In other words, 3mg may be an effective dose, but higher doses may be more effective.

In fact, most people who use Ostarine for the purposes of building muscle and improving body composition are using much higher doses.

Most people take Ostarine supplements in 12.5mg increments and 12.5-25mg/day for 4-6 weeks seems to be the preferred cycle dosage/structure.

Unfortunately, it’s not clear how safe higher doses are or what type of Testosterone suppression they cause.

It’s probably a good idea to take a solid PCT supplement after running a cycle of Ostarine, though you don’t necessarily need something as a strong as Nolvadex.

Is Ostarine Better For Cutting Or Bulking?

That really depends on your diet and your style of training.

In the world of performance enhancing drugs, some compounds have developed a reputation for producing leaner, dryer gains, but whether Ostarine will lean you out or bulk you up depends on how you eat.

If you place yourself in a caloric deficit, you’ll get pretty shredded.

If you up your caloire intake, you’ll bulk up.

Keep your calorie intake the same and you may get bigger AND leaner.

So, Ostarine can’t be classified as a ‘cutting agent’ or a ‘bulking agent’.  Whether you get super cut or bulk up depends entirely on other factors.

Does Ostarine Have Any Side Effects?

man with headache holding his head in his hands

One of major claims made about all SARMs, including Ostarine, is that they “don’t cause side effects” but research shows they’re not entirely harmless.

Ostarine, for example, doesn’t appear to cause much androgenic activity in the prostate (definitely a good thing), but does appear to cause some Testosterone suppression at doses of 1-3mg.

It’s possible that higher doses cause greater suppression, but there are no studies upon which to draw these kinds of conclusions.

It’s safe to say Ostarine is way less likely to cause side effects than steroids, but to say that it causes absolutely no side effects would be a lie.

In the Phase II clinical trial, some of the subjects reported headache, back pain, and nausea, but if you actually look at the data from the study, people taking placebos reported those same side effects.

Ostarine looks to be pretty safe at low doses, but we really have no idea what the health implications of taking higher doses for prolonged periods of time are.

Is Ostarine Legal?

There’s a lot of confusion about whether Ostarine is legal.  This should clear things up, though…

Ostarine is technically an unapproved drug and is illegal to sell as a dietary supplement, specifically for the purposes of human consumption.

It’s not a controlled substance though, so it’s perfectly legal to buy and possess.

If this seems confusing, that’s because it is.

You see, in the United States, there’s a legal gray area where drugs that have not been approved but are not controlled substances can be bought and sold as ‘research chemicals’.

They’re usually labeled ‘not for the purposes of human consumption’, but obviously, very few people who buy them are actually researchers looking to study them.

It’s just a way for companies to get away with selling unapproved drugs.

Legally, Ostarine is the Intellectual Property (IP) of GTX, the company that’s developing it.

Pharmaceutical companies may not care if people mess around with their creations while they still haven’t gained approval, but once a drug gains approval, anyone selling off-brand Ostarine is taking a chunk out of the bottom line.

Some SARMs have been abandoned, so it’s unlikely those companies will sue anyone over them, but for SARMs like Ostarine, it’s entirely possible.

As it turns out, pharmaceutical companies don’t take too kindly to other companies violating their intellectual property rights.

Where To Buy Ostarine

Like most chemicals, Ostarine comes from China and since Chinese chemical manufacturers aren’t necessarily held to strict purity and potency standards, quality become an issue.

Some manufacturers offer high quality, pure Ostarine.

Other’s don’t care about the quality of the product.

You’ll find a lot of companies selling Ostarine, but I personally wouldn’t trust most of them.

Read forums, ask questions, and go with a vendor who accepts credit cards.

The Bottom Line On Ostarine

man post ostarine cycle

Ostarine can help you pack on a few pounds of solid muscle and definitely comes with few side effects than steroids.

However, that doesn’t mean there are absolutely no side effects to be wary of.  Like steroids, Ostarine may suppress natural Testosterone production, especially at higher doses.

Unfortunately, higher doses haven’t been tested in humans, so it’s tough to say how much suppression we’re talking about.

If you’re interested in cycling a compound that will actually allow you to build a significant amount of muscle, check out the Best Muscle Builders list from some recommendations.

If you have any questions about anything, you can find me on Instagram and Twitter.  I’m always down to talk supps (and SARMs).

Have anything to add about Ostarine?  Comment Below

I’m Matt Theis, founder of SuppWithThat, Momentum Nutrition, and Singular Sport. I created SWT to separate the science from the hype and publish accurate, research-based information on supplements. If you like what I have to say here, feel free to check out my supplements at and

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