L-Citrulline is a freely available amino acid that is also found in foods such as watermelon. It is often used as a supplement in various situations, for example in the sports world.

No, it belongs to the non-essential amino acids. That means it does not necessarily have to be consumed through food, but supplementation is not excluded.

Essential amino acids must be obtained through food, because animal organisms cannot produce them themselves. Non-essential amino acids can be produced by the organism itself, but are sometimes also taken additionally via supplements.

There are 20 standard amino acids that are considered the building blocks of proteins. Of these, 9 are essential, the rest are non-essential or, under certain circumstances, semi-essential.