Know2eat

L-citrulline

Amino Acids & Proteins

What l-citrulline may help with

Ranked by how strong the human evidence is — best supported first.

Best supportedHealthy blood pressureModerate evidence· 4 sources

Then, in order

About L-citrulline

A non-protein amino acid found in watermelon and produced in the urea cycle. It bypasses intestinal and hepatic arginase and is converted to arginine in the kidney, which makes it a more efficient way to raise plasma arginine than arginine itself.

Citrulline is the rare case where the second-generation supplement genuinely improved on the first. Gram for gram it raises plasma arginine more than oral arginine does, because it escapes the first-pass degradation that destroys most of an arginine dose. The performance evidence that follows is modest rather than dramatic: meta-analyses report small improvements in high-intensity endurance and in repetitions to failure, with heterogeneous trials and effect sizes that would be hard to notice individually. The blood pressure data are similarly small and consistent.

Sold as
Powder, Capsule, Pre-workout blend component
Standardised to
Grams of free L-citrulline — distinct from citrulline malate, which is roughly half malate by weight — a product without this marker may not resemble what was studied.
Also known as
Citrulline, L-citrulline

Regulation: Sold as a dietary supplement with no pre-market efficacy review. Not prohibited in sport.

What the research used

The amounts, forms and durations published trials of L-citrulline actually administered.

These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.

  • Studied for Exercise performance

    3–6 g

    Limited

    L-citrulline, single dose 60 minutes before exercise

    Plasma arginine peaks around an hour after ingestion, which is why trials use this interval. Effects on performance are small and inconsistent between studies.

  • Studied for Blood pressure

    3–6 g

    Moderate

    Daily · 4–16 weeks

    Meta-analyses report reductions of a few millimetres of mercury. Consistent in direction, small in size.

This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.

When it was taken

Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.

Each timing below was actually compared against an alternative in a trial, which is unusual.

  • Before exercise

    Moderate

    Plasma arginine and nitric oxide markers peak roughly 60 minutes after an oral citrulline dose, and performance trials dose accordingly. The pharmacokinetics have been measured directly, which makes this one of the better-founded timing conventions in sports supplementation.

    Timing was tested. A trial compared this window against another and reported a difference.

The evidence in depth

Best supported: Moderate

What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.

Healthy blood pressure

Heart Health
Moderate evidence

Meta-analyses of citrulline supplementation report small but consistent reductions in systolic and diastolic blood pressure, larger in people with raised baseline pressure. The absolute effect is a few millimetres of mercury.

Moderate evidence. Several human studies point the same way, with real caveats.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Endothelial function

Circulation
Limited evidence

Trials report improvements in flow-mediated dilation and arterial stiffness with citrulline, most clearly in people with existing vascular dysfunction. Studies are small.

Limited evidence. Early human work, or mostly lab and animal research.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Exercise performance

Muscle & Physical Performance
Limited evidence

Meta-analyses report small improvements in high-intensity exercise performance and in repetitions completed during resistance training with citrulline or citrulline malate. Trials are heterogeneous and individual effects are small enough that many studies find nothing.

What may be going on: Citrulline escapes intestinal and hepatic arginase, is converted to arginine in the kidney, and raises nitric oxide availability more effectively than an equivalent oral arginine dose.

Limited evidence. Early human work, or mostly lab and animal research.

View the 4 sources

Deep research mode adds each paper’s own conclusion and stated limitations.

Things to know

Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.

  • Interaction

    Additive hypotension with nitrates and PDE5 inhibitors

    Interacts withNitrates, PDE5 inhibitors, antihypertensives

    Citrulline acts on the nitric oxide pathway. Combining it with nitrate medication or sildenafil-type drugs can lower blood pressure more than intended.

  • Worth knowing

    Caution after myocardial infarction

    The mortality signal from the arginine trial after heart attack was not tested with citrulline, but citrulline raises arginine by design. Extending the caution is the prudent reading rather than a demonstrated risk.

  • Too much

    Well tolerated

    Citrulline causes noticeably less gastrointestinal upset than arginine at equivalent effect, which is one of its practical advantages.

In the food catalogue

The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.

WatermelonThe food source citrulline is named after, though reaching a trial…

Evidence ratings on this page: 1 moderate evidence, 2 limited evidence.

Supplements are sold in the US without pre-market review of efficacy or safety. Nothing on this page is a recommendation to take L-citrulline, or a dose to follow.