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Citrulline

Citrulline

Best for

Improve nitric oxide balance

Large effect, needs confirmation 1–24 g/day <1–13 weeks 11 studies, n=252 #3 of 21 studied

Citrulline likely benefits exercise endurance and artery flexibility, offering modest support rather than making demanding workouts feel easy for most people.

Median effective dose, most-studied outcomes

  • Sustain more output for longer 8 g <1–9 wk
  • Help your vessels widen with blood flow 8.5 g 1–8 wk
  • Make hard exercise feel easier 7.5 g 1–6 wk
Full protocol, 7 outcomes

Risk, worst reported severity

  • bone fracture (tibia/femur) severe
  • giddiness severe
  • antihypertensives moderate
  • blood glucose lowering moderate
All 11 events and interactions

What citrulline actually does

Outcome Effect Evidence Dose Time Rank
Clear benefits 2
Keep going longer during exercise Likely benefit Exercise endurance helps you sustain effort before fatigue makes you slow down or stop.
moderate 		4 meta-analyses 16 papers · n=2.2k 1–12 g 0–9 wk #7 /42
Make arteries more flexible Likely benefit Flexible arteries help blood move smoothly and reduce strain on the heart.
moderate 		2 meta-analyses 13 papers · n=418 2–10 g 1–8 wk #4 /45
Worth watching 1
Improve nitric oxide balance Large effect, needs confirmation Nitric oxide helps blood vessels relax and maintain healthy circulation.
large 		12 RCTs 11 papers · n=252 1–24 g 0–13 wk #3 /21
Early research 3
Perform better in sport Not enough research Overall sport performance reflects how well you perform across the demands of your sport.
— 		1 RCT 1 papers · n=42 4.4 g — —
Feel less strain during exercise Not enough research Lower physical strain can leave more room to keep working when a session gets demanding.
— 		1 RCT 2 papers · n=— 6–10 g 4 wk —
Increase blood flow Not enough research The circulatory system carries oxygen and nutrients to tissues throughout the body.
— 		1 study 1 papers · n=— 6 g — —
Doesn't appear to help 1
Make exercise feel easier Doesn't appear to help Perceived exertion is how hard exercise feels to you as you are doing it.
trivial 		2 meta-analyses 10 papers · n=617 1–12 g 1–6 wk #1 /17

Effect tiers come from native-unit MCID where available, Cohen's d otherwise.

Protocol

Dose, timing & forms

How much

For the strongest practical targets, trials span roughly 1 to 12 g daily for sustained exercise output and 2 to 10 g daily for artery flexibility. Many endurance protocols cluster around 6 to 8 g, while vascular trials commonly use daily supplementation for several weeks rather than a one-off dose.23 More is not automatically better: the research does not show a dependable improvement in how easy exercise feels, even at higher tested amounts.3

When and how long

For training, take citrulline consistently and align the dose with the workout when your goal is endurance support. The useful signal in the research is repeat use across training periods, not saving it only for a big event.3 For vascular goals, treat it like a daily routine and judge results over weeks, since vessel-function trials measured changes after ongoing supplementation.2

Forms & standardisation

Look for a label that clearly identifies either L-citrulline or citrulline malate and states the amount per serving. Citrulline malate is common in workout products, but the evidence does not establish a universal advantage over L-citrulline alone.3 If you choose citrulline malate, check whether the label discloses the citrulline-to-malate ratio, since that determines how much actual citrulline you receive.

Studied range, by outcome

Outcome Studied range Median effective Duration Evidence
Sustain more output for longer 1–12 g 8 g <1–9 wk 16 papers 3 sig. endpoints
Help your vessels widen with blood flow 3–10 g 8.5 g 1–8 wk 11 papers 4 sig. endpoints
Make hard exercise feel easier 1–12 g 7.5 g 1–6 wk 10 papers 1 sig. endpoint
Promote easier vessel relaxation 1,000–2,400 mg 1,500 mg 1–13 wk 4 papers 2 sig. endpoints
Improve oxygen use in muscle 6 g — 4 wk 2 papers
Finish more reps or faster 4.4 g — — 1 paper
Restore blood flow through tiny vessels 6,000 mg 6,000 mg 4 wk 1 paper 3 sig. endpoints

Adverse events and drug interactions

Safety events

bone fracture (tibia/femur) severe
giddiness severe
Foetal ventriculomegaly (serious adverse event) severe
gastrointestinal symptoms (nausea, vomiting, flatulence) mild
Stomach discomfort mild
vaccination related adverse event mild
headache mild
gastrointestinal symptoms mild

Drug interactions

antihypertensives moderate unknown
blood glucose lowering moderate unknown
metformin minor increases effect
Buy well

Recommended Citrulline products

Real products that dose Citrulline where the research does, in a clean formulation, from brands we've audited. We only list ones we'd stand behind.

Chosen for adequate Citrulline dosing vs. the studied range, a clean formulation (grade A–C), and independent brand-quality audits. Not sponsored.

In context

What this is and how it works

  • Across 16 studies (n=2,154), citrulline improved time before fatigue.3
  • The reviewed evidence spans 49 papers and 90 outcomes, including 13 artery-flexibility studies involving 418 participants.2

Citrulline is an amino acid your body makes and that naturally occurs in foods such as watermelon. Unlike amino acids used to build muscle protein, its main supplement role is serving as a building block for arginine, which your body then uses to produce nitric oxide.1

Think of citrulline as a refill for your blood vessels' traffic-light system. It raises circulating arginine, giving nitric oxide production more raw material, and nitric oxide signals the smooth muscle around vessel walls to loosen so blood moves through more freely.1 This pathway fits the evidence suggesting benefits for vessel function and sustained exercise output, though results vary across protocols and populations.23

Bottom line

Citrulline is a sensible option if you want modest support for sustained exercise output or artery flexibility and you are willing to use it consistently.23 Do not buy it expecting every workout to feel easier, because the reviewed evidence does not support that promise.3 People using blood-pressure or blood-sugar medicines should check with a clinician before adding it.

Frequently asked

Common questions

What does citrulline do before a workout?

Citrulline raises the raw material your body uses to make nitric oxide, a signal that tells blood vessels to relax. Trials suggest it can support sustained exercise output, although it does not reliably make a hard workout feel easier in the moment.13

Is L-citrulline or citrulline malate better?

Both forms appear in exercise research. L-citrulline gives you citrulline alone, while citrulline malate adds malate, a compound involved in energy metabolism, but current evidence does not establish that the malate version consistently delivers better results.3

How long does citrulline take to work?

Workout studies often test citrulline around training sessions, while vascular studies assess daily use across several weeks. The endurance and artery-flexibility findings come from consistent use, not an occasional scoop.23

Does citrulline make exercise feel easier?

Not reliably. Across the reviewed trials, citrulline showed no meaningful overall reduction in perceived effort, even where some studies found improvements in exercise output.3

Sources

Sources

  1. 1. Oral L-citrulline supplementation increases plasma arginine concentration in humans (2007) ↑
  2. 2. Effects of L-citrulline supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials (2018) ↑
  3. 3. The effect of citrulline malate supplementation on muscle endurance: a systematic review and meta-analysis of randomized controlled trials (2019) ↑
  4. 4. Effect of citrulline on post-exercise recovery in trained male athletes: a randomized double-blind placebo-controlled trial (2010) ↑

Generated August 27, 2026

Related

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