OTR-AC (MK-2866 ESTER) Facts Explained!


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OTR-AC is a new, breakthrough sarm, taking the much-loved MK-2866 and adding an ester to it. This brings about all the same great benefits of Ostarine with some unique added properties that might just make it a better choice in certain scenarios! Learn all about OTR-AC below...

What is Ostarine?​

In order to fully understand what OTR-AC is, it is imperative to understand what Ostarine (Ostabolic) truly is (MK-2866, no ester).

Ostarine (which is sometimes sold under other names such as MK-2866 or Ostabolic) is a selective androgen receptor modulator (SARM). SARMs are designed to act specifically on androgen receptors. The benefit of this is that the effects will be exhibited in both muscle and bone, with limited side effects on other parts of the body.

Ostarine is one of the most well-studied and most popular SARMs on the market. At this time, GTx (who have been developing the SARM) have conducted over 8 clinical trials on MK-2866 on about 600 hundred subjects. Since the early 2000s, the discoveries made about Ostarine have led to it being used in bodybuilding.

What is OTR-AC?​

OTR-AC, also called MK-2866 Ester, is MK-2866 (Ostarine) which has undergone esterification during chemical synthesis to maximize the potency, bio distribution and half-life. The esterification of anabolic agents results in at least a 10-fold increase in half-life, which means that the active ingredient has the potential to remain bioactive ten times longer. This results in numerous benefits, such as decreased dosing frequency and more stable blood levels.

OTR-AC benefits​

In coming years, it is very possible that OTR-AC could replace or be more widely used than the original MK-2866 compound, due to the differences explained above which appeal to many users.

  • Maximise muscle growth
  • Increased bone density
  • Greater strength and performance
  • Improved recovery
  • Leaner and drier look

OTR-AC Cycle​

OTR-AC is dosed at 25-50 mg every other day, being that it has a longer ester. 50 MG every other day seems to be a sweet spot with some users going up to 100 mg every other day with no added side effects.

The longest that it is suggested to run an OTR-AC cycle is 12 weeks... It is important to give your body adequate time to recover and for hormone levels to return to normal before embarking on your next cycle.


While some people would often say Ostarine (Ostabolic) does not require PCT, this is not accurate information and a sarms mini pct would be required.


OTR-AC Elite is probably one of the most universally suitable SARMs you can find! From beginner to advanced, standalone or stacking, bulking or cutting, it can have a place. It is one of the most versatile and widely researched sarms and a favorite of many...

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