Your body produces citrulline during the urea cycle. It converts to arginine and boosts nitric oxide, which relaxes blood vessels. For workouts, L-citrulline or citrulline malate is taken 30 to 60 minutes before, often on an empty stomach to speed absorption. Many people use it to reduce fatigue and support cardiovascular health.
High doses may cause mild stomach upset. Citrulline can lower blood pressure, so those on blood pressure medication should consult a healthcare provider. Its effects during pregnancy and breastfeeding are not well studied.