L-Glutamine 500 mg by NOW® (glutamine) is considered an endogenous amino acid, which means that the body can synthesize it on its own. However, in some circumstances, the body may need more glutamine than it can produce. In the body, glutamine plays a key role in nitrogen metabolism and is essential for maintaining a healthy nitrogen balance. Glutamine also acts as the primary fuel for the rapidly growing cells of the immune system and digestive tract.