L-citrulline is naturally produced in the body via the urea cycle when carbamoyl phosphate is changed over to citrulline during the ornithine carbamoyltransferase reaction. The organic compound citrulline is an α-amino acid. Its name is derived from citrullus, the Latin word for watermelon, from which it was first isolated in 1930. L-citrulline is one of the many amino acids that the human body needs to survive. This amino acid helps to optimize the blood flow through the body by being converted to L-arginine and, later, nitric oxide. Nitric oxide is particularly important since it helps fight against physical and mental fatigue as well as sexual dysfunction. L-citrulline can also help detoxify the liver of ammonia and other compounds, and it may help relax blood vessels as well.

How is it Made?
Citrulline is made from ornithine and carbamoyl phosphate in one of the central reactions in the urea cycle. It is also produced from arginine as a by-product of the reaction catalyzed by NOS family (NOS; EC 1.14.13.39). Arginine is first oxidized into N-hydroxyl-arginine, which is then further oxidized to citrulline concomitant with release of nitric oxide.

Where is it Found?
The rind of watermelon (Citrullus lanatus) is a good natural source of citrulline. Citrulline is abundantly found in fish, meat, eggs, milk, watermelon and legumes. Foods rich in protein, also contain high amount of citrulline.

Benefits / Uses
Citrulline as a supplement helps the body to overcome fatigue and stress. The right amount of citrulline levels in the body promote increased energy and ensures normal functioning of the immune system. With deficiency in citrulline, fatigue becomes a common problem, thus preventing to achieve optimal health and wellness. Citrulline is often recommended for patients suffering from urine problem. Frequent urination, can be treated using this compound. It is capable of minimizing almost every problem related to excessive urination. Scientific studies have shown, that citrulline can reverse the gradual advancement of atherosclerosis (congestion of arteries). This could mean that citrulline is beneficial to people suffering from cardiovascular diseases.
Arginine aids in the production of nitric oxide in our body which promotes healthy flow of blood, thus contributing to overall health. The heart finds it difficult to pump blood, if adequate amounts of nitric acid is not produced. Intake of arginine supplements keep nitric oxide at optimum level. Citrulline supplements help to facilitate production of arginine, as citrulline is converted into arginine into our body. Including citrulline in the diet can increase stamina, and boost physical activity. There are some citrulline supplements that are known as sexual enhancers. Doctors advice to use them for sexual improvement. So, if you want to spice up your life taking citrulline capsules, as prescribed by your healthcare professional, would definitely be a good option.

Dosage
The recommended daily supplemental dose of L-Citrulline is 200-1000 mg once a day before bed (at the same time of the day when you ought to be taking your L-Arginine supplement). L-Citrulline supplements may be difficult to find on their own as they are most likely going to be combined with L-Arginine or included as a part of a collection of supplements meant to do a number of specific things. This is why the dosage amount can vary so greatly. The lowest recommended daily dose is the 200 mg while the most that you will want to take in a 24 hour period should not exceed 1000 mg. You will need to keep this in mind especially if thus supplement is combined with other supplements that are taken in high doses or more than once throughout the day.

Possible Side-Effects / Precautions / Possible Interactions
So far citrulline side-effects have not been reported in clinical results or medical literature. However, there is not enough reliable scientific information to know if L-citrulline is safe to take during pregnancy or while breast-feeding. Until more is known, avoid L-citrulline while you are pregnant or breast-feeding.

Research Studies / References