You have heard of the SARM Ostarine (MK-2886) but the similar ACP-105 is rising in popularity as a contender to eclipse Ostarine’s position as one of the most popular SARMs out there.

Often used as a beginner’s cycle, Ostarine is a mild SARM with a host of positive benefits with mild testosterone suppression and relatively low side effect profile.

However, the new ACP-105 appears to be a fresher, more potent version of Ostarine without so many of the negatives.

And ACP-105 also appears to offer other nootropic benefits in addition to its muscle-growing properties.

But it must be considered that research on ACP-105 is scarce in comparison to Ostarine.

Ostarine (MK-2886)

Ostarine, otherwise known as enobosarm or MK-2866, is a selective androgen receptor modulator (SARM) that was initially developed as a means to combat muscle wastage and osteoporosis, by mimicking the effects of testosterone. Since its creation at the turn of the millennium by GTx Inc., ostarine has been used in a variety of clinical trials for conditions including post-menopausal tissue wastage, tissue wastage in lung and prostate cancer sufferers and even urinary incontinence.


The ostarine molecule (C19H14F3N3O3)

What interests us here, of course, is ostarine’s properties for healthy individuals seeking strength and fitness benefits. 

So: can ostarine actually confer such benefits? 

The answer is a very firm ‘yes’; but as with all the other SARMs in this series – ligandrol, RAD140, cardarine and andarine – ostarine has specific uses and will suit some more than others.

Ultimately, you must know who you are, and that includes whether you are male or female, and what you want to achieve, before deciding on which SARM to take. You must also be in no doubt of the potential risks and side effects, which we will discuss below.

ACP-105 is available from our trusted vendor SWISS CHEMS. Use the code “HS11” to get 11% off all SARMS on their website.

The Lowdown — What it Can Do For You


Ostarine is often referred to as the ‘most anabolic’ SARM, and it’s for this reason that bodybuilders, strength athletes (powerlifters, Olympic lifters, strongmen), practitioners of contact sports, martial artists and gymbros are the ones you’ll find taking it.

All of these groups seek the following benefits:

  • Loss of unwanted body fat
  • Increased lean muscle mass (even in a caloric deficit)
  • Increased energy levels
Jon Anthony SARMs results
Jon Anthony SARMs results in 2 months

ACP-105 is available from our trusted vendor SWISS CHEMS. Use the code “HS11” to get 11% off all SARMS on their website.

How ostarine works

SARMs induce anabolic activity – growth – by directly stimulating the body’s androgen receptors. These are specific sites within the body to which androgenic (i.e. male) hormones, including testosterone and androsterone, bind. 

The activity of these androgen receptors, and the binding of androgens to them, is crucial to the proper expression of male characteristics, including muscle growth and reproductive function.

In the womb, androgens are responsible for sexual differentiation, and then during puberty they regulate the development and function of the penis, prostate and other sexual organs, as well as inducing growth spurts, larynx development and growth of skeletal muscle.

For adults, androgens regulate behaviour, the production of sperm, muscle growth, bone function and aspects of the cardiovascular system.

Androgens regulate sexual function and are responsible, in part, for aggressive behaviour in men. As a result, disregulation or blocking of the androgen receptors can lead to all sorts of conditions. 

Ostarine binds to the androgen receptors and mimics the effects of testosterone, increasing protein synthesis and therefore muscle growth.

This is also what steroids do, but SARMs generally have an advantage over steroids, because they only bind to receptors in skeletal muscle tissue.

Steroids, by contrast, work on other tissues in the body and have, as a result, been linked to all sorts of side effects, including prostate and heart problems.

SARMs are also non-aromatising, meaning that they are not converted to estrogen by the body in an attempt to maintain the body’s testosterone-to-estrogen balance.

By contrast, aromatisation can occur when using steroids or testosterone injections, which upset that balance, leading to problems such as gynecomastia (formation of breast tissue) which are ubiquitous among irresponsible amateur lifters.

Although there is no certified research on the use of this SARM for bodybuilding purposes, research in other contexts indicates that ostarine can significantly enhance lean muscle mass for both men and women [R]. 

Even with a dose as low as one milligram, ostarine can have significant effects.

A study on muscle-wasting in cancer patients showed that a one-milligram dose of ostarine led to a substantial increase in power climbing stairs, and those administered higher doses saw even greater effects [R].

Again, this is strong evidence for ostarine’s muscle-building effects.

Animal trials have also indicated that Ostarine can increase bone density and prevent bone loss, which should be of interest to weightlifters in general, but especially to those who lift heavy weights and are therefore at increased risk of bone injuries including fractures [R].

Of course, it would be strange for athletes and competitors to be taking ostarine, and running the risk of being caught, if it didn’t have the desired effect.


ACP-105 is a new selective androgen receptor modulator (SARM), made by Acadia. The manufacturer claims that ACP-105 has as potent an anabolic effect as testosterone in in-vitro assays. In pre-clinical trials, ACP-105 has demonstrated a powerful affinity for skeletal muscle, making it a true SARM.

As with RAD 150, another new SARM we’ve recently written about, there isn’t a great deal of clinical information on ACP-105 compared with other SARMs like Ostarine. What there is, though, is certainly promising.


Before we go into more detail about ACP-105, first we’ll give you a quick run-through of what SARMs are and how they’re used. If you want to read about SARMs in detail, we recommend consulting our one-stop primer on them, which features as part of our Ultimate Series on SARMs.

ACP-105 is available from our trusted vendor SWISS CHEMS. Use the code “HS11” to get 11% off all SARMS on their website.

How Strong is ACP 105?

Derek of More Plates More Dates fame has analysed the few studies of ACP-105, including these two (one – two) and has the following to say about ACP 105.

“The % of anabolic activity was determined to be 67%, with only 21% reversal of the prostate gland (which is used to measure androgenic activity).

From this we can conclude that this SARM has an anabolic:androgenic rating/ratio of 3.19:1

There are several SARMs that have anabolic:androgenic ratios of 3:1 and up though, so this is fairly typical.

While we can vaguely gather what we can expect from this compound (the comparisons that come to mind are Ostarine and S4), without knowing the binding affinity of the compound we can essentially only make shot in the dark guesses.

We do know what kind of interaction ACP-105 has with the androgen receptor though, which helps shed light on things a bit more.

Based on the information that was available, we know that ACP-105 is a partial agonist.


Full agonists induce greater levels of suppression, but are more potent (based on the information presented).

Partial agonists on the other hand, are less suppressive, but are typically weaker relative to Testosterone and DHT, which is the case with ACP-105.

A fairly low concentration of ACP-105 attaches to the androgen receptor better than DHT does, and is blatantly weaker than Testosterone and DHT in general.

In one sense, this is a disappointment as we are all awaiting the release of the end all be all SARM that is only exerts minor suppression, has minimal/zero androgenic side effects, and can rival or beat Testosterone in overall anabolic activity.

This is asking a lot though, and it would be more useful to simply compare ACP-105 to the other most promising mainstream SARMs to determine if it has a place in a researchers up and coming test protocols.”

So it looks like ACP-105 is more or less similar to Ostarine and Andarine in terms of anabolic performance.

The second study, in which mice that had and hadn’t been given ACP-105 were exposed to radiation and the results compared, also suggests that administration of the SARM may have motor-skill benefits such as increased speed, endurance, balance and coordination.


There’s not a huge amount of info on ACP 105 available, because of how new it is

The studies available on ACP 105 suggest an equivalent human dosage of around 11mg a day. Although there isn’t a great deal of information available, a dosage of 10-15mg a day seems to be agreed upon.

It’s worth noting that like Stenabolic, ACP-105 has a short half-life, which means that you may have to administer it up to three times a day, as the Redditor below notes. This may prove inconvenient for some, and lead them to prefer a SARM with a longer half-life like Ostarine.

Which is Better?

At present, we are reliant on anecdotal evidence over clinical studies.

However, ACP-105 appears to be a better choice over Ostarine because the following:

  • More anabolic
  • High bioavailability
  • Less liver toxic
  • Less suppressive
  • Shorter half-life

But Ostarine appears to edge out ACP-105 on the following:

  • Cheaper
  • More clinical studies
  • Longer half-life, less redosing
  • Better lipid profiles after blood work
  • More information on it
  • Greater availability

As always, we do not condone nor condemn the use of SARMs. Albeit, we do recommend that you thoroughly research each compound before initiating a cycle. A good place to start would be on our master article broaching the topic here.


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