Vit.O.Best L-Citrulline 1000 is a nutritional supplement in capsule form containing L-citrulline, an amino acid found naturally in foods such as watermelon. L-citrulline is primarily used to improve athletic performance and endurance by helping to increase the body's production of nitric oxide, which in turn improves blood circulation and the delivery of oxygen and nutrients to muscles during exercise. It has also been shown that L-citrulline can help reduce muscle fatigue and speed recovery after training.