Unflavored Power Nitric Oxide Booster Amino Acid If you're looking for a quality pre-workout supplement, L-Citrulline is a good choice. This natural amino acid boosts nitric oxide production in the body, leading to better blood flow and improved athletic endurance. It can also help support cardiovascular health and promote heart health. Additionally, L-citrulline fortifies immune function and contributes to sexual wellness and better libido.