Ostarine (MK-2866) 📗 Full User’s Guide | Sep 2023

Ostarine MK 2866

This article is the ultimate, full A-Z guide of Ostarine, otherwise known as MK 2866, or Enobosarm. In this guide, we'll cover everything you need to know, like:

  • What Is Ostarine?
  • How Does it Work?
  • Ostarine Dosage Protocol
  • Ostarine Cycle Examples
  • Ostarine Side Effects
  • Is PCT Required?
  • What Results to Expect
  • …and much, much more!

I've been in the SARMs industry, as a user myself, since 2010, and I hope that this article clears up some common misconceptions you may have about Ostarine (MK 2866).

If you're in a hurry, you can just use the table of contents to find the exact answer you're looking for—or, if you just want to buy Ostarine, click the big button to see my recommended SARMs vendors (I've tried each one myself).

So, with that in mind, let's get to it!

What is Ostarine (MK-2866)?

Ostarine (MK-2866 Molecular Structure)

Ostarine, also known as MK-2866, is a type of SARM, or selective androgen receptor modulator. Ostarine is one of the safest, and most well-researched SARMs in existence.

Some of the proven benefits of Ostarine (MK-2866) are:

  • Enhanced Muscle Growth
  • Rapid Fat Burning
  • Prevents Muscle Loss
  • Increased Strength
  • Improved Bone Density
  • …and more

We'll go over all the Ostarine benefits later in this article, and explore what the clinical trials and evidence have to say, but for now, let's explain more about how Ostarine works.

Mechanism of Action

How does Ostarine work? The same way that all other SARMs work. The reason that SARMs such as Ostarine and others are so unique, is that they mimic the effects of anabolic steroids, WITHOUT the numerous side effects that come with them.

Your body has androgen receptors everywhere:

  • Bicep Muscles
  • Tricep Muscles
  • Pectoral Muscles
  • Heart Muscles
  • Leg Muscles
  • Intestine Muscles

Basically any muscle tissue in your body has androgen receptors. These receptors are just waiting for a hormone or compound to “bind” to them, signaling for them to grow.

Ostarine vs. Steroids

Now, say you want to inject some testosterone and take some dianabol. These are two common anabolic steroids that fitness enthusiasts take to gain muscle.

Now, when you ingest or inject anabolic steroids, they bind to your body's androgen receptors, which is why they're so effective at improving lean muscle and athletic performance.

But, here's the problem – anabolic steroids aren't selective in nature. So, they will bind to your bicep muscle androgen receptors, and make them bigger, but they will also bind to your heart and organ muscle tissues, and make them bigger, too.

This causes all kinds of problems and side effects for steroid users, but fortunately with SARMs like Ostarine, this is a thing of the past. The reason they're called “SARMs” or selective androgen receptor modulators, is because they're selective in nature.

This means they only bind to the “good” androgen receptors, like the muscles you WANT to grow (biceps, triceps, legs, etc.) called skeletal muscles. They AVOID the muscles you DON'T want to grow, like organ muscle tissues, heart muscles, intestine muscles, etc.

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This is why SARMs are so popular nowadays. They get you the same fat loss, and muscle building effects as steroids, with maybe only 5-10% of the side effects.

In short, they're a wonder drug.

History of Ostarine

GTx Pharmaceuticals

Despite Ostarine being such an amazing compound for weight loss and muscle gains, it wasn't discovered by bodybuilders until around 2010 or so. In fact, it was actually first developed in 1997 by GTx Incorporated, to help cancer patients suffering from muscle loss. [R]

Here is a timeline of Ostarine's development:

  • 1997 – Ostarine (MK 2866 or Enobosarm) first developed, with the goal of treating muscle wasting in cancer patients suffering from cachexia (rapid muscle loss)
  • 2007 – Ostarine reaches phase II in clinical trials, and after partnering with Merck (the pharmaceuticals titan), GTx received a whopping $45 million for research [R]
  • 2016 – Despite numerous evidence of the benefits of Ostarine, the FDA decided to reject the phase III clinical trials, and GTx went back to the drawing board [R]

Ostarine is still currently in development, so it isn't FDA approved quite yet, although GTx is still researching Ostarine (MK 2866) for other purposes.

That being said, bodybuilders know EXACTLY what its uses are (wink wink, nod nod).

Is Ostarine legal? That's an interesting question, but the short answer is “yes.” Ostarine is currently legal to buy and sell online, and is legal in every country except Australia.

Ostarine is classified as a “research compound,” which means it's legal to buy and sell for “research purposes” online. So, basically, as long as you don't literally take Ostarine liquid right in front of a cop, you will be 100% okay.

Ostarine is legal to buy and possess in the following countries:

  • United States
  • United Kingdom
  • South Africa
  • Canada
  • Singapore
  • India
  • South America

In short, Ostarine is legal everywhere except Australia. That being said, many of my Australian friends have used Ostarine and other SARMs with zero problems.


Ostarine is considered a Schedule 4 Prescription Drug by the TGA, the Therapeutic Goods Administration, which is basically the FDA of Australia. [R]

What that means, is that if you get caught with Ostarine, and don't have a doctor's prescription for it, you're probably going to get in legal trouble.

Again, most of my Australian bodybuilding buddies take Ostarine and don't have any issues, just don't be an idiot and take it in public.

Professional Athletes

While Ostarine is still legal to buy and possess in most countries, keep in mind that the World Anti Doping Agency has still banned them, meaning they test athletes for this compound.

In fact, the following agencies have listed SARMs like Ostarine as banned substances:

  • World Anti Doping Agency [R]
  • US Anti Doping Agency [R]
  • Australian Sports Anti-Doping Authority [R]

With its ability to rapidly build muscle mass, shred body fat, and improve athletic performance, is it any wonder that Ostarine is banned, though? Not really.

Long story short, if you're a pro athlete, you may get tested for Ostarine, so it's best if you don't use it. Most professional agencies will test for it, since it is such an unfair advantage.

Military Members

Another question I get asked a lot is does the military test for Ostarine? The short answer is no. A normal military test will not detect Ostarine, although if they suspect you are taking anabolic steroids or SARMs, they may use a test that CAN pick it up.

Normal military drug tests will test for:

  • Marijuana
  • Amphetamines
  • Cocaine

So, for the most part, military men don't have to worry about SARMs. Just don't be an idiot and take them out in the open and you will be good to go.

Ostarine Benefits

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Now for my favorite part – the benefits of Ostarine. Thankfully, Ostarine is one of the most well researched SARMs out there, so there's no shortage of evidence here.

Dozens of clinical trials have confirmed the following benefits:

  • Build Lean Muscle Mass
  • Rapidly Shred & Burn Fat
  • Minimal Testosterone Suppression
  • Improved Bone Mineral Density
  • Increased Strength & Power
  • …and more

I personally experienced all of these benefits when I am on an Ostarine cycle, but let's go over each one and explore what the clinical studies and research has to tell us.

Rapid Muscle Growth

One of the most obvious and biggest benefits of Ostarine, is its ability to help users increase muscle mass in a very short period of time. In fact, I typically gain around 10-20lbs of muscle mass when I'm on a SARMs cycle of just 2-3 months.

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Ostarine has been clinically proven to enhance muscle growth. In fact, in one study, just 3mg (about 10% the normal dose) was given to 120 elderly patients, who didn't even workout or hit the gym, and they noticed massive increases in lean muscle mass [R]

“CONCLUSION: GTx-024 [Ostarine] showed a dose-dependent improvement in total lean body mass and physical function was well tolerated.”

In other words, Ostarine builds muscle and has few side effects.

Shreds Body Fat

Ostarine is generally known as a “cutting SARM,” although it can be used on a bulking cycle. It really shines when it comes to getting lean and cut, though. While there haven't been any clinical studies specifically studying fat loss on Ostarine, logically it makes sense.

If Ostarine boosts lean muscle mass growth, and helps with gaining muscle, where do you think those calories come from? From fat, of course. Ostarine uses either an excess of calories that you consume, OR existing fat mass on your body, to build new muscle tissue.

My first cycle I lost around 7-8 pounds of fat, and packed on 15 pounds of muscle, so it isn't hard to see that Ostarine has a fat burning effect that greatly helps body composition.

(I also wasn't even on a calorie deficit diet, I was on a calorie SURPLUS diet!)

While Ostarine isn't as good at shredding fat as a compound like RAD 140, Cardarine, or Stenabolic would be, it's still far more researched, and is generally considered to be the safest SARM that we know of right now.

Strength & Power

While, mg per mg, Ostarine is a relatively weak SARM, it still has a ton of data to suggest that it's great for improving strength and muscle mass in users. I personally noticed my lifts skyrocketed when I was on my first cycle of SARMS.

Here's how much my strength went up on a 3 month cycle of Ostarine:

  • Bench Press – From 225lbs to 285lbs
  • Deadlift – From 315lbs to 395lbs
  • Squat – From 235lbs to 305lbs
  • Overhead Press – From 125lbs to 185lbs

Overall, I'm very sensitive to SARMs, so your results might be worse (or better), but there's one thing for sure: Ostarine definitely helped build muscular mass and strength.

Bone Density & Tendons

Tons of clinical studies suggest Ostarine improves bone density. [R]

In fact, that's why it's currently being researched as a potential medication to help elderly women suffering from osteoporosis (brittle bones).

Not only that though, but Ostarine also helps improve tendon and ligament strength, which explains why it's so good at improving overall lifts. [R]

Stronger tendons and ligaments means your body can handle more weight, especially with compound lifts that stress the human body so much.

My Ostarine Review

Ostarine SR9009 Stack
4-Week Ostarine Cycle Results
READ MORE: 6 Shocking Ostarine Before And After Transformations

Overall, my Ostarine experience was extremely good. I suffered extremely minimal side effects (more on those later), built around 15lbs of muscle, and lost 7lbs of fat.

Here's the stats on my first Ostarine cycle:
  • Cycle Length: 12 Weeks
  • Ostarine Dosage: 25mg/day
  • Goal of Cycle: Recomposition
  • Workout Routine: 5-Day Split
  • On Cycle Support: Yes
  • Post Cycle Therapy: Yes
  • Muscle Gained: 15 Pounds
  • Body Fat Lost: 7 Pounds

Overall, it was a great cycle. I took an on cycle support and did post cycle therapy, which I'll talk about more later, but overall the results were great. My body fat percentage was way lower, and I was able to shred off that last layer of abdominal fat hiding my abs.

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If you want to learn more, you can read my Ostarine log.

Dosage & Cycle Facts

What's the best Ostarine dosage? The truth is there's no one “ideal dosage,” although in general with Ostarine (MK 2866) we recommend you start at 10mg/day as a beginner.

Here are the dosage guidelines for Ostarine:

  • Beginner Dose: 10mg/day
  • Intermediate Dose: 20mg/day
  • Advanced Dose: 30mg/day

As you can see, I took 25mg/day on my first cycle, which was close to an advanced dose. Most people will get great results on just 10mg/day though, especially if it's your first cycle.

Remember that ostarine has been proven to build lean muscles and improve muscle building on just 3mg per day, so even just taking 10mg is more than enough for beginners.

For more information, you can read my Ostarine dosage guide.

Ostarine Cycle Guidelines

In general, with SARMs, anabolic steroids, or any performance enhancing substances, you want to do what's called a “cycle.” This is where you take it for a certain period of time, and then get “off” the drug for a certain period of time, so you don't become dependent on it.

The best Ostarine cycle length is going to last either eight weeks or twelve weeks, depending on what your goals are (fat loss, build muscle, hit a certain bench press goal, etc.)

For your first cycle, I recommend just doing 10mg/day for 8 weeks.

That is more than enough to give you some great muscle gains, fat burning, and transform what your body looks like. You can literally go from “zero to hero” with that cycle.

Ostarine Stacks

Now onto the good stuff – Ostarine stacks. A “stack” is a term that refers to any anabolic steroid, SARM, or investigational drug that you combine with others.

The reason people “stack” legal steroids and SARMs is to get the best of both worlds. By taking a fat burning SARM with a muscle mass building SARM, you can amplify the effects.

Here are two sample Ostarine stacks for beginners:

MK 2866 Bulking Stack

Take this stack if your main goal is to improve protein synthesis, pack on slabs of lean body mass, build strength, and just get bigger in general. Eat tons of calories while you're on it.

Ostarine bulking stack for 8-12 weeks:

This stack will give you increased bone density, improved recovery, less muscle aches after an intense workout, improved blood flow for better pumps, and much, much more.

MK 2866 Cutting Stack

A cutting cycle is if your main goal is fat loss and muscle dryness, creating that “cut and shredded” look that so many bodybuilders and fitness influencers love.

Ostarine cutting stack for 8-12 weeks:

This cutting cycle will give you insane weight loss, will shred that subcutaneous fat (that hides your abdominal muscles), and will also build muscle too (even in a calorie deficient diet).

Ostarine PCT Guide

Does Ostarine require a PCT? To be honest, there's no straight answer. Ostarine will affect your natural testosterone levels differently than mine. Every human is different, and the testosterone reduction may be mild for others, and moderate for some.

In general, research shows that Ostarine does suppress testosterone production, but only about 10% as much as steroids do. Still, a bare bones Ostarine PCT is useful.

What is a PCT? It stands for “Post Cycle Therapy,” which in this case is just a series of dietary supplements and compounds taken after your cycle, to get your testosterone production totally back to normal.

Personally, I recommend Testomax. Just one bottle is all you need.

Where to Buy Ostarine

JAMA Fake SARMs Quality Report
Only around 10% of SARMs companies actually sell pure SARMs, according to laboratory reports

You have to be careful when buying any selective androgen receptor modulators (SARMs) or anabolic steroids online, because tons of companies sell fake stuff that will cause liver damage and other nasty side effects. You certainly don't want that, and neither do I.

We have several places we recommend you get SARMs from, but so far, our favorite place has been Chemyo. Every batch of their Ostarine MK 2866 is 3rd party tested for the utmost purity, so you can rest assured that what you're getting is pure MK 2866.

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Most companies don't have an independent laboratory test for their purity, because they'd probably be embarrassed at the results. This is why you only want to buy from companies that have actual tests. This shows they stand behind their products.

Furthermore, if you use the code “SARMsFacts” you'll get 10% off your entire order.


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In summary, Ostarine MK 2866 is an amazing compound that I would compare to taking a mild anabolic steroid, except with far less side effects.

The half life is relatively short, so it will kick in the first week pretty quickly.

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Frequently Asked Questions
❓ How Fast Does Ostarine Kick In?

Thanks to its short half life of roughly 24 hours, Ostarine MK2866 starts working within just 1-2 days. Peak blood concentrations will not occur for about 1 week, which means that you won't feel the full effects of Ostarine until 7 days.

❓ How Much Ostarine Should I Take?

According to clinical evidence, you will build muscle on just 3mg of Ostarine per day. With this in mind, much of the bodybuilding community recommends you take 10mg/day of Ostarine MK 2866 as a starting dosage.

❓ Does Ostarine Suppress Testosterone?

Studies have shown that yes, Ostarine exerts a dose-dependent effect on testosterone suppression. This is no cause for concern, though, as researchers noted that testosterone production returns to normal within 30 days after your cycle.

❓ How Long Does Ostarine Stay in Your System?

Ostarine MK 2866 has a half life of 24 hours, which means it's out of your system within 2-3 days. It's a very fast acting SARM, which means it will both get into your system and out of your system very quickly.

❓ How Safe is Ostarine?

According to studies, Ostarine MK 2866 is very well tolerated by most test subjects. More research should be done on the long term side effects, but overall, most experts consider Ostarine to be very safe and effective.

LEGAL DISCLAIMER: The information on this page is intended for entertainment and information purposes only. It is not a substitute for professional medical advice. Always check your local jurisdiction’s laws before buying anything or doing anything.

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1 thought on “Ostarine (MK-2866) 📗 Full User’s Guide | Sep 2023”

  1. Which SARMS have ever displayed negative effects on kidney function? Which of the SARMS have been accounted as being cancer causing, and I know there are a few of those from clinical research.


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