L-arginine
"L-arginine is an amino acid. Amino acids are the building blocks of proteins and divided into essential and nonessential categories. Nonessential amino acids are made in the body, but essential amino acids are not. As such, they must be provided through dietary intake. L-arginine is considered semi-essential or conditionally essential, meaning that it becomes essential under certain circumstances and conditions, including pregnancy, infancy, critical illness, and trauma" - healthline