L-Citrulline Is the Main Ingredient in Nitric Oxide Supplements

November 24, 2025 •

3 min read

While nitric oxide itself is a gas produced naturally by the body, supplements are formulated with precursors that help the body create more of it. L-citrulline is the primary ingredient often used in these supplements to raise nitric oxide levels effectively.

Quick Summary

This article explores L-citrulline, its conversion process to L-arginine, and why it's a superior choice over L-arginine for boosting nitric oxide. It details the mechanisms of action, benefits for performance and health, and compares it with other common ingredients like beetroot extract.

Key Points

L-Citrulline Is Most Effective: Supplements use precursors, and L-citrulline is considered superior to L-arginine due to its excellent absorption and efficient conversion process.
Nitrates Are Another Option: Ingredients like beetroot extract work through a different, oxygen-independent pathway to increase nitric oxide levels.
Better Bioavailability: L-citrulline avoids extensive metabolism in the gut and liver, leading to more stable and higher levels of L-arginine in the bloodstream.
Performance and Health Benefits: Increased nitric oxide from supplements can enhance athletic endurance, speed up recovery, and support cardiovascular health through improved blood flow.
Fewer Side Effects: L-citrulline is generally associated with fewer gastrointestinal side effects compared to direct L-arginine supplementation, particularly at higher doses.
Synergistic Formulas: Many effective supplements combine L-citrulline with other ingredients like beetroot extract, which can offer synergistic benefits for boosting nitric oxide.

What Is the Main Ingredient in Nitric Oxide Supplements?

The main ingredient used to create nitric oxide (NO) in supplements is L-citrulline, an amino acid that acts as a precursor to L-arginine, which the body then uses to produce NO. This indirect pathway is more efficient than supplementing with L-arginine directly, which has poor bioavailability and is often broken down in the gut before it can be used for NO production.

Nitric oxide is a critical signaling molecule involved in various physiological processes, most notably vasodilation, which is the widening of blood vessels. This increased blood flow helps transport more oxygen and nutrients to muscles and tissues throughout the body, improving exercise performance, heart health, and recovery.

The Role of L-Citrulline and the Conversion Process

Unlike L-arginine, L-citrulline is not broken down in the gut and is efficiently absorbed into the bloodstream. The kidneys then convert L-citrulline into L-arginine, leading to a more consistent and sustained increase in plasma L-arginine levels. This process is what makes L-citrulline the superior ingredient for reliably boosting nitric oxide levels.

Comparison of Common Nitric Oxide Precursors

To understand why L-citrulline is often preferred, it is useful to compare its properties with other common nitric oxide-boosting ingredients.


Feature	L-Citrulline	L-Arginine	Beetroot Extract (Nitrates)
Effectiveness at increasing NO	High; reliably raises NO via conversion to L-arginine.	Variable; poor absorption and breakdown limit effectiveness.	High; converts to NO, especially in low oxygen conditions.
Absorption	Excellent; bypasses gut metabolism for higher plasma levels.	Poor; significant portion is metabolized in the digestive system.	Very good; follows the nitrate-nitrite-NO pathway.
Side Effects (Dosage > 10g)	Low incidence of gastrointestinal distress.	Higher risk of bloating, diarrhea, and stomach pain.	Generally safe, but can cause harmless red urine and stool.
Timing of Effect	Delayed onset due to conversion, but provides sustained effect.	Rapid spike and fall due to poor bioavailability.	Acute effects seen within hours of ingestion.

How Nitric Oxide Supplements Work

Nitric oxide supplements work by providing the body with the necessary building blocks to naturally increase its production of NO. These supplements do not contain actual nitric oxide gas but instead supply precursors like L-citrulline, L-arginine, or nitrates.

Amino Acid Pathway: This pathway relies on the enzyme nitric oxide synthase (NOS) to convert the amino acid L-arginine into nitric oxide. Since L-citrulline is efficiently converted to L-arginine in the kidneys, it effectively feeds this pathway, leading to a steady and reliable increase in NO levels.
Nitrate-Nitrite Pathway: This is an independent pathway where dietary nitrates, found in foods like beetroot, are reduced to nitrites by bacteria in the mouth. These nitrites are then converted to nitric oxide in the body, particularly in conditions of low oxygen, such as during intense exercise.

Key Benefits of Nitric Oxide Supplements

The increased blood flow and vasodilation resulting from higher nitric oxide levels offer a range of potential benefits, especially for athletes and those concerned with cardiovascular health.

Improved Exercise Performance: Higher blood flow delivers more oxygen and nutrients to working muscles, which can enhance endurance, increase power output, and reduce fatigue.
Faster Recovery: The enhanced circulation aids in removing metabolic waste products like lactic acid and ammonia from the muscles more efficiently, which can reduce muscle soreness and speed up recovery times.
Cardiovascular Health: By relaxing and widening blood vessels, nitric oxide helps regulate blood pressure and improves overall heart and vascular health. This may be particularly beneficial for individuals with high blood pressure.
Erectile Dysfunction (ED) Support: Nitric oxide plays a crucial role in erectile function by relaxing smooth muscles in the penis, which is necessary for achieving an erection. L-citrulline has shown promise in improving mild-to-moderate ED symptoms.

Conclusion: Making an Informed Choice

While several ingredients can boost nitric oxide, L-citrulline stands out as a highly effective and well-tolerated precursor. Its superior absorption and efficient conversion to L-arginine make it a reliable choice for increasing nitric oxide levels to support athletic performance, cardiovascular health, and recovery. When selecting a supplement, consider options featuring L-citrulline or beetroot extract, and always consult a healthcare provider to ensure safety and determine the best approach for your individual needs. A balanced, nitrate-rich diet is also a foundational way to support natural nitric oxide production.

Frequently Asked Questions

No, nitric oxide supplements do not contain the gas itself. Instead, they provide precursor compounds like L-citrulline or nitrates, which the body can convert into nitric oxide.

L-citrulline is generally considered more effective than L-arginine for raising nitric oxide levels. L-citrulline has better absorption and bypasses the gut's metabolic processes that quickly break down L-arginine.

Beetroot extract is a natural source of dietary nitrates. When consumed, these nitrates are converted by the body into nitric oxide, helping to relax and dilate blood vessels.

Yes, they can. The increased blood flow from higher nitric oxide levels helps deliver more oxygen and nutrients to muscles, which can enhance endurance, boost power, and reduce fatigue, especially in moderately trained individuals.

By promoting vasodilation, nitric oxide helps relax and widen blood vessels. This effect can lead to lower blood pressure and improved overall blood flow, which supports heart and vascular health.

Side effects can vary by ingredient. High doses of L-arginine may cause gastrointestinal issues like bloating and diarrhea, while beetroot extract can cause harmless discoloration of urine and stool. Serious side effects are rare but possible, so consultation with a doctor is recommended.

Many foods are rich in nitric oxide precursors. A diet high in leafy greens, beets, and protein sources can support natural production. However, supplements are a concentrated and convenient way to achieve doses often used in clinical studies for specific performance or health goals.