OTR-AC, also known as MK-2866 Ester, is MK-2866 (Ostarine) that has undergone esterification (the process of combining an organic acid with an alcohol). This chemical process is used to maximize the potency and extend the half-life (the time it takes for an amount to reduce to half its original value) of a substance. This process gives the ester version of ostarine the ability to remain bioactive ten times longer. This results in benefits such as reduced dosing frequency and more stable blood levels.

How OTR-AC Works
As the ester version of the selective androgen receptor modulator (SARM) ostarine, OTR-AC is more potent and has longer lasting effects. By binding to proteins in the body known as androgen receptors, it stimulates the formation of muscle tissue. This in turn leads to an increase in muscle mass and strength.

Research into OTR-AC
Increase in Muscle Mass and Strength
Studies suggest that OTR-AC, along with other SARMs, increases muscle mass and strength by stimulating muscle tissue formation:

• In adult rats, administration of SARMs, including OTR-AC, resulted in an increase in lean muscle mass and a decrease in body fat percentage. 
• In aged male and female rats, administration of OTR-AC resulted in an increase in lean muscle mass, decreases in fat mass, and significant improvements in their ability to climb stairs.
• Studies showed that OTR-AC can help increase muscle mass in rats with cancer cachexia (muscle loss). 
• In aged male and female rats, OTR-AC significantly improved total lean body mass and physical function. 
• In rats that had their ovaries surgically removed, OTR-AC improved muscle tissue. 
• In rats, OTR-AC increased muscle mass by increasing muscle cell production. 

Reduction of Body Fat
In addition to helping you gain muscle mass, OTR-AC has also been found to reduce overall body fat:

• In Phase I and II clinical trials, OTR-AC has shown promising results in increasing total lean body mass, decreasing total tissue fat percentage, and improving functional performance. 
• A review of studies showed that OTR-AC may help increase lean body mass and decrease body fat in overweight rats. 
• In a Phase 2a study, administering OTR-AC along with other SARMs resulted in an increase in lean fat mass and a decrease in body fat percentage. 
• In male rats, OTR-AC increased the breakdown of fat cells by improving fat metabolism and affecting the release of adiponectin (a hormone that regulates the breakdown of fatty acids). 

Improving Bone Health
Studies suggest that OTR-AC may help stimulate bone formation and protect against bone diseases:

• In rats that had their ovaries surgically removed, administration of OTR-AC resulted in improved bone healing. 
• In a rat model of age-related osteoporosis in male rats, both OTR-AC and testosterone treatments improved bone healing by increasing callus volume and surface area, bone volume and density, and bone width. 
• In a rat model of postmenopausal osteoporosis, high doses of OTR-AC for 5 weeks resulted in an increase in bone volume, density, and bone mineral density. 

Reduction in Cholesterol Levels
Evidence suggests that OTR-AC may help lower cholesterol levels, especially low-density lipoprotein (bad cholesterol):

• In aged male and female rats, administration of OTR-AC resulted in a significant reduction in low-density lipoprotein levels. 
• In rats that had their ovaries surgically removed, treatment with OTR-AC reduced blood levels of cholesterol.