Creatine monohydrate is a natural substance that can be converted into creatine phosphate in the body. Creatine phosphate helps make a substance called adenosine triphosphate (ATP). ATP provides energy for muscle contraction; one of the most commonly used supplements that people use to build lean muscle mass, maximize performance, and increase strength. Creatine monohydrate is the most popular and effective fitness supplement on the market today because it can quickly increase muscle size and strength.