You can’t take nitric oxide directly as a supplement. Nitric oxide is a gas your body produces on its own, so “nitric oxide supplements” actually contain precursor ingredients that your body converts into nitric oxide. The three main approaches are supplementing with L-arginine, L-citrulline, or consuming dietary nitrates from foods like beetroot. Each works through a different biological pathway, and how you take them matters for results.
How Your Body Makes Nitric Oxide
Your body has two distinct pathways for producing nitric oxide. The first uses the amino acid L-arginine: your cells take up L-arginine and, in the presence of oxygen, convert it into nitric oxide through a series of enzyme reactions. This is the pathway that L-arginine and L-citrulline supplements target.
The second pathway works in reverse, starting with dietary nitrates found in vegetables like beets, spinach, and arugula. When you eat nitrate-rich foods, your salivary glands concentrate the nitrate in your saliva at levels 10 to 20 times higher than in your blood. Bacteria living on your tongue then convert that nitrate into nitrite. After you swallow, about half the nitrite reaches your stomach’s acidic environment and gets converted into nitric oxide, while the rest is reabsorbed into your bloodstream and converted in your tissues later. This pathway is especially active when oxygen levels in tissues are low, making it a useful backup system during exercise.
L-Citrulline vs. L-Arginine
Both amino acids end up as raw material for nitric oxide, but they aren’t equally effective. About 60% of the L-arginine you swallow gets broken down in your gastrointestinal tract, and another 15% is metabolized in your liver. That means roughly 30% of supplemental arginine actually reaches your bloodstream. L-citrulline bypasses this problem because it isn’t broken down in the gut or liver. Instead, your kidneys convert it into arginine, which then feeds nitric oxide production.
Research in animal models found that citrulline supplementation raised blood arginine levels 35% more than the same amount of arginine supplementation. Citrulline also increased the actual flow of arginine through the body, while arginine supplements did not. For this reason, L-citrulline is generally the more efficient choice if your goal is sustained nitric oxide support.
L-Arginine Dosing
For cardiovascular benefits like blood pressure support, studies have used 3 to 12 grams per day in people with mild hypertension. A meta-analysis covering trials that used 4 to 24 grams daily (with a median dose of 9 grams) over 2 to 24 weeks found reductions in both systolic and diastolic blood pressure. For exercise performance, the effective range is lower: around 1.5 to 2 grams per day taken consistently over weeks.
L-Citrulline Dosing
Pure L-citrulline is commonly taken at 3 to 6 grams per day. Citrulline malate, which combines citrulline with malic acid, is typically dosed at 6 to 8 grams, though it’s worth noting that the malate portion makes up a significant share of that weight. A dose-response study in healthy adults tested 2, 5, 10, and 15 grams of citrulline and found that larger doses produced greater increases in plasma levels. For most people, 3 to 6 grams of pure L-citrulline is a reasonable starting range.
Dietary Nitrates From Food
Beetroot juice is the most studied dietary source of nitrates for boosting nitric oxide. A standard 70 mL shot of concentrated beetroot juice contains about 400 mg of nitrate. Circulating nitrate has a half-life of roughly 5 hours, so a single dose provides a relatively long window of activity compared to amino acid precursors.
Other high-nitrate foods include spinach, arugula, celery, and lettuce. However, concentrated beetroot juice is the easiest way to get a consistent, measurable dose. One important detail: because oral bacteria play an essential role in converting nitrate to nitrite, using antibacterial mouthwash can actually block this pathway and reduce the benefits of dietary nitrate intake.
When to Take Each Form
Timing depends on whether you’re using nitric oxide precursors for exercise or for general cardiovascular support.
For exercise, take L-citrulline or citrulline malate 30 to 60 minutes before your workout. This gives your body time to convert the citrulline into arginine and then into nitric oxide. Beetroot juice works on a slightly longer timeline. Most exercise studies have participants drink it 2 to 3 hours before activity, which aligns with the time needed for the nitrate-nitrite-nitric oxide conversion in saliva and gut.
For general blood pressure or cardiovascular support, consistent daily intake matters more than precise timing. L-arginine can be split across two or three doses throughout the day to maintain steadier levels, since a large single dose faces significant breakdown in the gut. L-citrulline is more forgiving and can be taken once or twice daily.
What the Blood Pressure Effects Look Like
In a clinical trial of hypertensive patients, a single dose of a nitric oxide-donating lozenge reduced systolic blood pressure by 4 points and diastolic by 5 points within 20 minutes. After one hour, both systolic and diastolic pressure dropped by an average of 6 points from a baseline of 144/91 down to 138/85. These are modest but meaningful reductions, especially for people with mildly elevated blood pressure.
Protecting Nitric Oxide After It’s Made
Producing nitric oxide is only half the equation. Free radicals, particularly superoxide, can neutralize nitric oxide before it has a chance to relax your blood vessels. Vitamin C acts as a scavenger of these free radicals, protecting nitric oxide from being broken down too quickly. It also supports the enzyme that produces nitric oxide in your blood vessel walls. Eating vitamin C-rich foods (citrus, bell peppers, berries) alongside your nitric oxide precursors can help maintain higher effective levels.
Polyphenol-rich foods like dark chocolate, green tea, and pomegranate work through a similar antioxidant mechanism. Pairing your beetroot juice or citrulline supplement with these foods creates a more complete strategy than taking a precursor alone.
Nasal Breathing and Natural Production
Your body also produces nitric oxide in the paranasal sinuses, the hollow spaces behind your nose. When you breathe through your nose, you inhale this self-produced nitric oxide into your lungs, where it dilates blood vessels and improves oxygen transfer. In healthy subjects, blood oxygen levels were 10% higher during nasal breathing compared to mouth breathing. In intubated hospital patients, adding nasal air samples to their breathing supply increased arterial oxygen levels by 18%.
This means something as simple as breathing through your nose, especially during light to moderate exercise, provides a small but real nitric oxide benefit without any supplement at all.
Who Should Be Cautious
Because nitric oxide lowers blood pressure, people who already have low blood pressure or are taking blood pressure medications should start with lower doses and monitor their response. The combination of a nitric oxide precursor with blood pressure-lowering drugs can cause excessive drops in pressure, leading to dizziness or lightheadedness.
People with heart failure involving left ventricular dysfunction face a more specific risk: nitric oxide can worsen fluid buildup in the lungs and cause dangerous drops in heart rate and blood pressure in this population. Anyone taking medications for erectile dysfunction should also exercise caution, since those drugs work by amplifying the nitric oxide pathway and stacking supplements on top can cause a sharp blood pressure drop.