SupplementsAmino AcidsCitrulline

Citrulline

L-citrulline

The amino acid found in watermelon, and a better way to raise arginine than swallowing arginine.

Get a protocol
A pale L-citrulline capsule
Builds up
About a week
In your body
1-2 hour peak
Per 1 capsule
500 mg
30-day supply
$7.50One capsule a day, plus packing and delivery

What is citrulline?

L-citrulline is an amino acid, but not one your body uses to build protein. Instead it's a go-between. Your body makes it, passes it to your kidneys, and they turn it into arginine, which your blood vessels use to make nitric oxide.

Watermelon is the famous food source, and it holds more of it than most things you'd eat. Even the rind has some. You'd need quite a lot of melon to reach the amounts used in studies, though, which is why people use capsules.

Ours holds 500 mg of L-citrulline per capsule, with no animal products.

What it does

  • Blood flowSupports healthy circulation by feeding your body's nitric oxide supply.
  • Arginine levelsHelps maintain healthy arginine levels in your blood.
  • ExerciseSupports high-intensity exercise performance.
  • Waste handlingPart of the cycle your body uses to clear ammonia.

These statements have not been evaluated by the FDA. This product is not intended to diagnose, treat, cure or prevent any disease.

The full guide · 15 min readL-citrulline supplement benefits and side effects: what the evidence showsWhich form, how much, when to take it, and whether it's worth it, with the studies behind each answer.

What people take it for

How long it takes

It works fast and doesn't stockpile. A week of use was enough to raise arginine levels in studies, with the biggest change at the largest amounts.

Arginine in your blood after citrullineTypical pattern
Arginine peaks at 1 to 2 hours
Coming back down
08 hours
  1. 1 to 2 hoursArginine peaks in your blood
  2. 1 weekArginine levels stay higher through the day, at large amounts
  3. 1 to 17 weeksHow long the blood pressure studies ran

How long it stays in your body

We don't have a clean half-life figure from the studies we read. What's well measured is that arginine in your blood peaks about 1 to 2 hours after citrulline.

What's in a capsule

One capsule holds 500 mg. Blood pressure studies used 3 to 9 g a day, and the erection study used 1.5 g a day, so one capsule holds less than those.

The long way round, which works better

Arginine has a problem: your gut breaks most of it down before it reaches your blood. Citrulline doesn't have that problem. It gets past your gut and liver largely untouched and then your kidneys turn it into arginine. So taking the indirect route raises arginine more than taking arginine itself.

Very little is wasted. Even at very large amounts, less than 5% left in urine. Your kidneys do have a limit, though: at the top amounts studied, citrulline itself kept rising while arginine rose less than expected, and study authors think the kidney's conversion was full.

Citrulline was even named after watermelon, whose plant name is Citrullus. In one study, adults who drank watermelon juice for 3 weeks had 12 to 22% more arginine in their blood, which shows food can do the same thing.

Read the full guide to citrulline

What it interacts with

Goes well with

Side effects

  • Usually none. In a study of 2 to 15 g at a time, nobody reported side effects, and neither did the men in the erection study.
  • Large amounts of arginine and related amino acids can upset your stomach, so it's worth watching for this.

Check first if

  • Pregnancy or breastfeeding: there isn't enough safety data, and our label says to check with your physician.
  • Low blood pressure: citrulline may lower it further, so talk to your doctor first.
  • Kidney disease: your kidneys do the converting, so talk to your doctor first.

The blood tests that go with it

Work it out

Water falling through fine glassKidneys and electrolytes · CalculatoreGFR calculatorKidney filtration from creatinine, age and sex.One clear drop falling from a glass pipetteKidneys and electrolytes · CalculatorBUN to creatinine ratio calculatorThe ratio, in US or SI units.A taut Achilles tendon pushing off the groundBody and fitness · CalculatorVO2 max calculatorFrom your heart rates, or a 12-minute run.Two fingertips on the pulse at a wristHeart · CalculatorHeart rate zones calculatorYour five zones, Zone 2 included.

Supplementation

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These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease.

Want it more precise? Get the app.

A page can only tell you about Citrulline. The app tells you about you: whether it fits, when to take it, and whether it's working.

  • Checked against your blood work and everything you already take
  • On your daily timeline, around your sleep, training and meals
  • Followed over time, so you can see what moved
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Questions

What is L-citrulline good for?

Mostly blood flow, blood pressure, hard short efforts and erection hardness in men. Most of the research is early or mixed.

How long does L-citrulline take to work?

Arginine peaks 1 to 2 hours after a dose. Levels stayed higher after a week of large amounts. Blood pressure studies ran from 1 to 17 weeks.

What are the side effects of L-citrulline?

Usually none. Studies of large amounts reported no side effects, though they were small and short, and stomach upset is possible.

Is L-citrulline better than L-arginine?

For raising arginine in your blood, yes, because your gut doesn't break it down first. Arginine has more research on blood pressure, though.

Does watermelon have citrulline?

Yes, it's the richest common food source, and it's where citrulline got its name. In one study watermelon juice raised blood arginine by 12 to 22% over 3 weeks.

Who should not take L-citrulline?

Check first if you take nitrates, erection medicines or blood pressure medicines, have low blood pressure or kidney disease, or are pregnant or breastfeeding.

Can I take L-citrulline every day?

Blood pressure studies gave it daily for up to 17 weeks. We know less about longer use.

Can I take L-citrulline with Viagra?

Only if your doctor says so. Both can lower blood pressure, and together it could drop too low.

What is the half-life of L-citrulline?

The studies we read didn't give a clean number. It isn't stored, and very little leaves in urine because your kidneys turn most of it into arginine.

Sources
  1. Schwedhelm E et al. Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine. Br J Clin Pharmacol, 2008.
  2. Moinard C et al. Dose-ranging effects of citrulline administration on plasma amino acids and hormonal patterns in healthy subjects. Br J Nutr, 2008.
  3. Allerton TD et al. l-Citrulline supplementation: impact on cardiometabolic health. Nutrients, 2018.
  4. Barkhidarian B et al. Effects of L-citrulline supplementation on blood pressure. Avicenna J Phytomed, 2019.
  5. Mirenayat MS et al. Effect of L-citrulline supplementation on blood pressure. Curr Hypertens Rep, 2018.
  6. Luo X et al. Does l-citrulline supplementation and watermelon intake reduce blood pressure in middle-aged and older adults? Clin Nutr ESPEN, 2025.
  7. Trexler ET et al. Acute effects of citrulline supplementation on high-intensity strength and power performance. Sports Med, 2019.
  8. Harnden CS et al. Effects of citrulline on endurance performance in young healthy adults. JISSN, 2023.
  9. Viribay A et al. Effects of citrulline supplementation on different aerobic exercise performance outcomes. Nutrients, 2022.
  10. Cormio L et al. Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction. Urology, 2011.
  11. Collins JK et al. Watermelon consumption increases plasma arginine concentrations in adults. Nutrition, 2007.
  12. Rimando AM, Perkins-Veazie PM. Determination of citrulline in watermelon rind. J Chromatogr A, 2005.
  13. Rouge C et al. Manipulation of citrulline availability in humans. Am J Physiol Gastrointest Liver Physiol, 2007.

Written by LifeFrom from these sources, and not yet reviewed by a clinician. Talk to your doctor before starting a supplement.

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