L-Citrulline vs L-Arginine for Nitric Oxide & Blood Pressure
Educational summary — not medical advice. Use caution with blood-pressure meds, nitrates, or PDE5 inhibitors (Viagra/Cialis).
The counterintuitive winner is L-citrulline. Arginine is the direct building block for nitric oxide — but swallowed as a supplement, most of it is destroyed by the gut and liver before it reaches your blood. L-citrulline slips past that first-pass metabolism and is converted to arginine in the kidneys, so it actually raises blood arginine more than arginine itself does. For blood pressure, the honest effect is ~4 mmHg systolic (not the retracted "7.5 mmHg" figure that circulates online).
Why the direct precursor loses
It seems backwards that citrulline beats arginine at raising arginine. The reason is first-pass metabolism: oral L-arginine is heavily broken down by the enzyme arginase in the intestine and liver, so only a fraction reaches circulation, and high doses tend to cause GI upset before they move nitric oxide much. L-citrulline isn't a substrate for arginase; it's absorbed intact and converted to arginine in the kidneys, raising plasma arginine steadily. In a double-blind crossover pharmacology study, oral citrulline increased plasma arginine and nitric-oxide–dependent signaling more effectively than oral arginine (Schwedhelm 2008). That single finding is the core reason modern nitric-oxide supplements shifted from arginine to citrulline.
Blood pressure: real but modest — and beware the retracted number
Citrulline's nitric-oxide effect translates into a modest blood-pressure benefit. The credible meta-analyses put it at about −4.1 mmHg systolic (Barkhidarian 2019) to −4.5 mmHg (Yang 2019), with the diastolic benefit reaching significance mainly at ≥6 g/day, and larger effects in people with elevated baseline pressure.
Correction to what you'll read elsewhere A widely-quoted figure that citrulline lowers systolic pressure by ~7.5 mmHg comes from a 2019 meta-analysis that was formally retracted in 2021 (retraction notice). Many supplement pages still cite that number; it shouldn't be trusted. The honest, non-retracted figure is roughly 4 mmHg — real and worthwhile, but smaller.
When arginine (or both) still makes sense
Arginine isn't useless — it's just an inefficient oral nitric-oxide precursor. There's evidence that combining citrulline and arginine raises plasma arginine and nitric-oxide markers faster and higher than either alone (Morita 2014), which is why some pre-workouts pair them. For most people, though, plain citrulline is the simpler, cheaper, better-absorbed choice, and the combo isn't clearly worth the added cost for general use.
Which to buy, and how much
- For nitric oxide / blood pressure: L-citrulline, 3–6 g/day (≥6 g for the diastolic benefit), for at least 6 weeks.
- For pre-workout "pump": ~6–8 g citrulline (or ~8 g citrulline malate, which is ~5 g citrulline) about an hour before training.
- Skip high-dose arginine alone for nitric oxide — it's the less-absorbed, more GI-upsetting option.
- Buy on cost per gram of actual citrulline — see the ranking and mind the malate math.
Frequently asked questions
Is L-citrulline better than L-arginine for nitric oxide?
Yes, for an oral supplement — counterintuitively. Oral arginine is largely destroyed by gut/liver arginase; citrulline bypasses that and raised plasma arginine more than arginine itself in a crossover study (Schwedhelm 2008).
Does L-citrulline lower blood pressure?
Modestly — ~4 to 4.5 mmHg systolic in the credible meta-analyses, strongest at ≥6 g/day for ≥6 weeks. The widely-quoted 7.5 mmHg figure is from a retracted paper and shouldn't be trusted.
Should I take citrulline and arginine together?
The combo can raise nitric-oxide markers more than either alone, but for most people plain citrulline is simpler, cheaper, and better absorbed. The combination is optional, not necessary.
Related
- L-citrulline dosage guide — dose by goal + cost calculator
- Citrulline malate 2:1: how much is actually citrulline?
- Best L-citrulline — ranked by cost per actual gram
Sources
- Schwedhelm E, et al. "Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism." Br J Clin Pharmacol. 2008. PMID: 17662090
- Barkhidarian B, et al. "Effects of L-citrulline supplementation on blood pressure: a meta-analysis." Avicenna J Phytomed. 2019. PMID: 30788274
- Yang HH, et al. "Effect of oral L-citrulline on brachial and aortic blood pressure." Nutr Metab (Lond). 2019. PMID: 31889969
- Retraction Note: Mahboobi S, et al. "Effect of L-citrulline supplementation on blood pressure." J Hum Hypertens. 2021. PMID: 31690817 (the source of the widely-cited ~7.5 mmHg figure — retracted).
- Morita M, et al. "Oral supplementation with a combination of L-citrulline and L-arginine rapidly increases plasma L-arginine and enhances NO bioavailability." Biochem Biophys Res Commun. 2014. PMID: 25445598
- Winer N, et al. "Oral citrulline supplementation in pregnancies with preeclampsia: a multicenter RCT." Am J Clin Nutr. 2025. PMID: 39638148