Ornithine is a non-essential amino acid that plays a central role in the urea cycle, functioning along with arginine and citrulline to rid the body of ammonia, a by-product of protein metabolism. Because ornithine is converted into arginine, it can help to maintain healthy arginine levels in the body. Ornithine can also be converted into other amino acids, such as citrulline, proline, and glutamate, as well as creatine, an important muscular energy source.