§.01How NO supplements actually work.
Nitric oxide is produced via two pathways:
- L-arginine pathway: the enzyme nitric oxide synthase (NOS) converts L-arginine to NO + L-citrulline.
- Nitrate pathway: dietary nitrate (NO3-) is converted by oral bacteria to nitrite (NO2-), then to NO in tissues, especially under hypoxic conditions.
These work in parallel and are partially complementary. The pathway your supplement targets matters more than the brand on the label.
§.02Why L-arginine alone is mostly a waste.
Oral L-arginine is heavily metabolized by intestinal arginase in first-pass metabolism. By the time it reaches systemic circulation, the dose is dramatically reduced. Studies measuring plasma L-arginine after oral doses confirm: you need very large oral doses (10+ grams) to raise plasma levels meaningfully, and even then the effect on NO is inconsistent (Bode-Böger et al., 2007).
L-citrulline bypasses this: it is absorbed efficiently, then converted to L-arginine in the kidneys, raising plasma L-arginine more than L-arginine itself does.
§.03L-citrulline: the dose and the use case.
- Dose: 6 to 8 grams of L-citrulline (or 4-5 grams as citrulline malate) 30-60 minutes pre-workout.
- What it does: modestly improves pump (vascular dilation), reduces fatigue during high-rep training, and may extend time to exhaustion (Pérez-Guisado & Jakeman, 2010).
- What it does not do: dramatic strength increases (that is creatine), large endurance gains (that is training adaptation), or chronic cardiovascular improvement.
§.04The nitrate pathway: beetroot.
Dietary nitrate (~500 mg, equivalent to a glass of beet juice or several cups of leafy greens) raises plasma nitrite for several hours, which converts to NO in tissues. This pathway:
- Lowers oxygen cost of submaximal exercise.
- Modestly extends endurance.
- May modestly lower blood pressure with daily intake.
The supplement form (beetroot concentrate, beet juice powder) works; the dietary form (eating leafy greens + beets) works at least as well and contributes to general cardiovascular health.
Mouthwash kills the bacteria that convert dietary nitrate to nitrite.
If you use antimicrobial mouthwash daily and eat lots of leafy greens, you may be partially undoing your dietary nitrate benefit. Switch to a non-antimicrobial mouthwash or skip the antimicrobial rinse if you are dietary-nitrate-dependent.
§.05Stacking and timing.
For pre-workout pump and endurance: combine 6 g L-citrulline with 500 mg of beetroot nitrate, 30-60 minutes before training. The two pathways are complementary and the combined effect is modestly larger than either alone.
For ongoing cardiovascular benefit: diet beats supplements. A daily serving of leafy greens or beets contributes more sustainably than any pre-workout product.
Do not stack with: ED medications (sildenafil, tadalafil) without a clinician's input — additive hypotension risk. Or with nitroglycerin / isosorbide (cardiac nitrates) — same issue.
§.99The bottom line.
For workout pump and exercise endurance: 6 to 8 grams of L-citrulline 30-60 minutes pre-workout, optionally combined with 500 mg of beetroot nitrate. Skip L-arginine alone (first-pass metabolism destroys most of it). For cardiovascular health long-term, dietary nitrate (leafy greens, beetroot) consistently outperforms any single supplement. The supplement is for acute exercise effect, not chronic vascular health.
Nitro Pump (L-citrulline + beet) — at the apothecary.
Reviewed by Dr. Marthe Janssen, PharmD. Last updated May 19, 2026.
Disclaimer: this article is educational and does not substitute for advice from your prescriber. Statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure, or prevent any disease.