Ostarine Side Effects: How Safe is MK-2866?

Ostarine side effects

Is Ostarine safe? How bad are the side effects? I remember being so confused the first time I did an Ostarine cycle. I wanted to pack on lean muscle mass, but wanted to be safe.

Thankfully, according to research, Ostarine MK 2866 is one of the safest SARMs (selective androgen receptor modulators) that there is. But, that doesn't mean it has no side effects.

In today's article, you'll learn:

  • Is Ostarine Safe?
  • What Are The Ostarine Side Effects?
  • Does Ostarine Cause Hair Loss?
  • Does Ostarine Cause Testosterone Suppression?
  • Does Ostarine Cause Gyno?
  • Does Ostarine Shrink Your Balls?
  • Does Ostarine Cause Erectile Dysfunction?
  • Does Ostarine Cause Mood Swings?
  • Does Ostarine Cause Acne?
  • …and much, much more

I've been taking MK 2866 to build muscle mass and enhance fat burning for years now, so I've experienced pretty much every side effect possible. Now, without further ado, let's get started.

Is Ostarine Safe?

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Before we get too deep into the side effects, I want to make something clear: Ostarine is generally considered to be extremely well tolerated and very safe by studies. [R]

If you take the recommended Ostarine dosage of 10mg-20mg/day, you will most likely experience little to no side effects. You may experience some, but very few.

It's only when you start stacking SARMs and taking the upper limits of dosages that you begin to notice side effects like acne, gyno, testosterone production shutting down, and more.

Of course, ultimately, fitness enthusiasts (myself included) take SARMs at your own risk. While there is an enormous amount of data suggesting that the health benefits of Ostarine far outweigh any adverse effects, there still isn't enough long-term research studies to be sure.

Again though, that being said, I experienced almost no negative effects from Ostarine when I took it between the recommended dosages of 10mg and 20mg/day.

Common Side Effects

Before I dive into a list of every single Ostarine MK 2866 side effect ever reported, let's first just go over the most common adverse effects people experience. I see no need for you to worry yourself about all the insane MK 2866 adverse effects that could happen, unless you plan on taking a stupid dose that's 3x what I recommend.

When you take Ostarine MK-2866 within the recommended dosages of 10mg to 20mg/day, these are the most common side effects you will experience:

  • Mild Testosterone Suppression
  • Increased Cholesterol Levels
  • Slight Blood Pressure Increase
  • Higher Estrogen Level

Thankfully, these are all extremely easy to fix by taking some simple dietary supplements. I will discuss that later in this article, but for the most part, when you're taking Ostarine MK 2866 for muscle building, at a reasonable dosage, those will be your only sides.

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Full List of Ostarine Side Effects

Like I said, while I experienced insane lean muscle growth, body fat shredding, and enhanced athletic performance on my first Ostarine MK 2866 cycle, I experienced almost no sides.

That being said, I did experience a few. Before I walk you through each side effect and how to avoid them, let's first list all the side effects you might potentially have. This doesn't mean you'll actually experience them, especially within normal dosages.

Here is a full list of EVERY Ostarine side effect ever reported:

  • Hair Loss & Hair Thinning
  • Acne & Oily Skin
  • Low Testosterone Production
  • Erectile Dysfunction
  • Gynecomastia (Male Breast Cancer)
  • Smaller Testicles (Shrinking Your Balls)
  • Anxiety & Sleeplessness
  • Jaundice (Yellow Skin from Liver Failure)
  • Increased Blood Pressure
  • Increased Cholesterol & Lipid Profile
  • Increased Estrogen Levels
  • Lowered Libido
  • Headaches

Now, according to clinical trials, most of these side effects will only occur at the extreme end of Ostarine MK 2866 dosages, like upwards of 50mg/day.

Hair Loss

Does Ostarine cause hair loss? It can, but typically only on high dosages.

The reason for this is, as the Ostarine MK 2866 binds to androgen receptors in the body, it pushes testosterone out into the blood stream. Testosterone levels are high, and it gets converted into DHT, which binds to the scalp and causes hair loss.

This side effect typically only occurs at over 30mg/day.

Acne & Oily Skin

Can Ostarine cause acne? Absolutely. It's not nearly as bad as anabolic steroids, but on my first Ostarine cycle I noticed mild acne. Nothing major at all, it was literally just a couple pimples on my back, nothing was on my face.

Some people report very oily skin when taking dosages upwards of 30mg/day.

Low Testosterone Levels

Can Ostarine suppress testosterone levels? Absolutely 100%. You will likely experience a little bit of this, regardless of the dosage, which is why I always recommend an Ostarine PCT.

As the Ostarine MK 2866 binds to androgen receptors in the human body, it pushes testosterone out into the blood stream. This “tricks” your body into thinking your natural testosterone levels are too high, so it lowers the production to equalize blood levels of test.

This is 100% normal and happens on anything that increases muscle mass, from selective androgen receptor modulators like Ostarine, to anabolic steroids like Dianabol or Testosterone Enanthate, to designer steroids and everything in between.

Erectile Dysfunction

Can Ostarine MK 2866 cause erectile dysfunction? Yes, but typically only at higher dosages and when taken for extended periods of time (over 12 weeks). This is why we do not recommend an Ostarine cycle longer than 12 weeks for anyone.

Taking Ostarine MK 2866 for longer than 12 weeks will lead to your natural testosterone levels getting lower and lower, until your testicles completely shut down. Do not take SARMs for longer than 12 weeks, this is based on the past 10 years of experience I have with them.

Gynecomastia (Gyno)

Can Ostarine cause gyno? Yes, but it is not likely. Typically, you will only get gyno from Ostarine MK 2866 if you take it in very large amounts, for a long period of time.

Shrinking Testicles

Does Ostarine MK 2866 shrink your testicles? On normal dosages no, but on extremely high dosages of over 30mg/day taken for over 12 weeks, it is possible, yes.

The reason for this is that as your body stops producing testosterone while on cycle, your balls don't have to work anymore. So, they get “lazy” and basically shrink in size. This will return to normal after your cycle, and again, according to clinical trials, nobody experiences this adverse effect when they take Ostarine within the proper dosage (10mg-20mg/day).

Anxiety & Sleeplessness

Can Ostarine cause anxiety? Yes, but it is not a common side effect and does not appear to be dependent on the dosage taken. This appears to be a strange side effect that some people experience and others don't, likely due to genetic reasons.

Jaundice (Yellow Skin)

Can Ostarine cause Jaundice? Yes, but only in extremely high, and borderline lethal dosages, like taking over 100mg/day. Nobody should take this much Ostarine, ever.

Increased Blood Pressure

Can Ostarine increase blood pressure? Yes. This is one of the more common side effects of taking MK 2866. Generally speaking, any compound that improves lean body mass, physical performance, and helps you lose body fat, will increase blood pressure in high dosages.

The link between SARMs and blood pressure is not understood, although it is common knowledge for fitness enthusiasts and in the bodybuilding community that anabolic steroids and other anabolic compounds will typically increase your blood pressure. [R]

Increased Cholesterol

Can Ostarine increase cholesterol? Absolutely, yes. This is one of the most common side effects of Ostarine MK 2866 and pretty much any selective androgen receptor modulator out there. Why? Because cholesterol is a building block of lean muscle mass.

Cholesterol is used to make new cells, so what do you think happen when you take Ostarine, which turns your muscle growth into overdrive? Your body amps up the cholesterol production to make all this new lean muscle mass.

Don't worry, though. Your cholesterol levels will return to normal after cycle.

Increased Estrogen Levels

Can Ostarine cause increased estrogen levels? Absolutely, yes. It will cause this side effect in a very small amount at any dosage, but isn't a problem until taking over 30mg/day.

Here is why. I already explained how when you take Ostarine, it pushes testosterone away from androgen receptors and into your blood stream.

Well, most people don't know this, but over time, your body's natural testosterone levels get converted into other hormones, one of them being estrogen. So, the more Ostarine you take, the more testosterone gets pushed into your blood stream, the more gets turned into estrogen.

Again, just follow a proper MK 2866 post cycle therapy (PCT) and this will return to normal.

Lowered Libido

Can Ostarine lower libido? Yes it can, at high dosages taken for long periods of time. Your libido is caused by testosterone, so over time, with enough of a dosage, as your testosterone levels decrease, so will your libido.

This has never been a problem for me when I take reasonable dosages, however. It was only when I took a stack of 2 SARMs (Ostarine & RAD 140) at TWICE the normal dosage, for more than 12 weeks, that I noticed MILD libido decrease.

I could still have sex just fine, so I don't think lowered libido is a big concern for most.


Can Ostarine cause headaches? Yes, but not directly. Because Ostarine can increase your blood pressure, this can often lead to headaches. I will explain how to avoid this side effect using the right dietary supplements down below.

Avoiding Side Effects

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You want to pack on muscle tissue, lean body mass, experience rapid muscular growth, ripped muscles, and fat loss, right? WITHOUT any of the side effects of Ostarine MK 2866?

Here's how. While I can't help you if you decide to take insanely high dosages of Ostarine, by simply taking the following dietary supplements, you can avoid 99% of side effects.

Here is my personal “on cycle support stack” for Ostarine MK 2866:

  • Baby Aspirin (1 Per Day) – This lowers blood pressure and is proven safe in clinical trials
  • Citrus Bergamot (1200mg/day) – This is a natural herbal remedy that is great for lowering cholesterol levels and improving overall heart and artery health
  • Milk Thistle (300mg/day) – This is another natural herbal supplement that is great for liver health, liver detoxification, and helps your body process SARMs better
  • DIM (400mg/day) – This is a natural compound found in broccoli and cruciferous vegetables that helps process excessive estrogen and balance hormones

Taking this stack of supplements while on an Ostarine cycle or any other SARMs can drastically help you lower side effects, while still packing on lean body mass and pounds of muscle tissue.


In summary, Ostarine is by far the safest and most well researched selective androgen receptor modulator that there is on the market right now.

It's been shown to prevent muscle wasting, enhance muscle growth, improve bone density, strengthen bone and muscle tissue, and much more, according to clinical trials.

Ostarine MK 2866, however, is not without its side effects. You should be aware of the risks, even if it is mostly safe when taken in moderate dosages.

To still increase muscle mass and burn fat, in the safest way possible, I recommend you take the supplements I laid out above on any SARMs or Ostarine cycle you decide to take.

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.