L-Citrulline
An amino acid the body turns into arginine, best known as a pre-workout.
- Reps and hard sets
- Blood flow
- Soreness after training
- Endurance
- Blood pressure
- Muscle in later life
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is L-Citrulline?
L-citrulline is a non-essential amino acid: the body makes its own, and the richest food source is watermelon. As a supplement its job is to supply raw material for another amino acid, arginine, which the kidneys and the lining of the blood vessels build from it. It is sold as the plain amino acid and as citrulline malate, the same amino acid paired with malic acid, and it is one of the commonest ingredients in pre-workout powders.
Why do people take L-Citrulline?
Reps and hard sets
The thinking. This is the everyday reason people buy it: a scoop before training, so the last reps of a heavy set come easier. The idea is that more arginine in the blood means more nitric oxide, the signal that widens blood vessels, so muscle gets more blood under load.
What research has found. Nearly all of this research used citrulline malate, six to eight grams an hour before training. Reviews pooling it report small average advantages: one covering thirty trials and 644 people found a small overall gain, another about three extra repetitions before muscles gave up. A review of maximal strength alone found no clear difference. A fair body of trials has looked at this, and most point the same way.
Blood flow
The thinking. The pump, that tight and full feeling in a working muscle, is a large part of what people are buying here, along with circulation generally. Citrulline raises blood arginine more reliably than arginine itself does, because it slips past the gut and liver.
What research has found. A review of eight trials in 176 middle-aged and older adults found the artery lining widened better, though overall artery stiffness did not shift. Small trials in middle-aged men and postmenopausal women measured improvements too, while two run alongside a vibration-training programme found no difference. Measurements taken during exercise itself are fewer, and they disagree. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Soreness after training
The thinking. The day after is the other thing people mention: the stiff, sore feeling that follows an unusually hard session. Two ideas sit behind it — more blood moving through the muscle, and citrulline’s place in the urea cycle, the route the body uses to clear ammonia.
What research has found. One pooled analysis of thirteen trials in 206 people, most taking eight grams of citrulline malate within two hours of exercising, found lower ratings of how hard the effort felt and less soreness a day or two later. Blood lactate did not shift. Research here is still young: a few studies so far, mostly pointing the same way.
Endurance
The thinking. Cyclists, runners and rowers come at it differently: not the last rep, but holding a pace already near the edge. The same vessel-widening idea applies, with more oxygen reaching muscle for the same effort. These trials mostly used plain L-citrulline, two to six grams a day for a week.
What research has found. Two pooled analyses, one covering nine trials in 158 active adults, measured how long people lasted and how fast they covered a set distance, and found no clear difference. Individual trials point the other way: a week at 2.4 grams a day took 1.5 per cent off a four-kilometre cycling time trial in trained men. Only a few studies have measured this so far, though they mostly agree.
Blood pressure
The thinking. Away from the gym, citrulline has a following among people keeping an eye on their blood pressure. Nitric oxide relaxes the muscle in artery walls, and citrulline is a steadier way to raise its raw material than arginine itself, most of which the gut and liver take apart first.
What research has found. Three reviews have pooled this work, all in middle-aged and older adults. Two found average falls of about four millimetres of mercury in the upper reading and two and a half in the lower, larger where pressure was already high; an earlier review found no clear difference. The trials ran four to eight weeks. A reasonable number of trials have measured this, and most of them agree.
Muscle in later life
The thinking. The last group is people in their sixties and seventies, taking it with muscle and mobility in mind rather than a personal best. Beyond blood flow, the background reviews describe a second idea: citrulline appears to nudge the signalling that switches on protein building inside muscle.
What research has found. Two reviews of trials in adults over fifty, one of them covering 250 people, reported gains in muscle mass, in lower-limb strength and in a six-minute walking test, largest where citrulline and exercise were combined. A six-week trial in 44 people aged 60 to 73 found walking speed improved while strength did not shift. This is early work, a small number of studies, mostly pointing the same way.
What does L-Citrulline do in the body?
Citrulline is not really the active ingredient; it is the delivery method. The body converts it into arginine, and the lining of the blood vessels uses arginine to make nitric oxide, a gas that signals the muscle in artery walls to relax. Wider vessels carry more blood to working muscle.
The obvious question is why not simply take arginine. The answer is the gut and the liver: most arginine swallowed as arginine is taken apart before it reaches the bloodstream, while citrulline passes through both untouched and is converted later, in the kidneys and in the vessel lining itself. Gram for gram it raises blood arginine roughly twice as well.
What do people say about taking L-Citrulline?
These are anecdotes people have shared, not evidence.
What people like
- Very commonly, a better pump: the tight, full feeling in a working muscle, and several rate it above other blood-flow ingredients they have tried.
- Several report an extra repetition or two on a hard set, and a couple say recovery between sessions felt easier.
- Cost comes up repeatedly as the reason people keep buying it: bought as plain powder rather than capsules, it is cheap.
- One long-standing user outside the gym describes steady blood pressure readings over several years, taken daily in split amounts rather than before training.
Common complaints
- Taste is by far the commonest complaint: the malate form is called sour and hard to get down, and some switch forms over it.
- Next commonest is noticing nothing at all: several tried it for weeks or months and could not tell it from taking nothing.
- A couple describe an early effect that faded within weeks, and stopped buying once they worked out the cost of a full serving.
- The loose powder pulls in moisture and sets into a solid lump in the tub; one whole thread was given over to fixing that.
How people take it
- Amounts mentioned run from about six to twelve grams, taken roughly an hour before training, sometimes with more sipped during the session.
- Opinion splits between the two forms: the plain amino acid is preferred for taste and price, the malate for training.
- The few taking it for blood pressure rather than the gym split the day’s amount into two or three doses on an empty stomach.
- Most mix it into a pre-workout drink with several other ingredients, and a few say that makes its own effect impossible to judge.
Read from these public discussions:
- Citruline Malate and NO boosters (Slowtwitch forum, 2012)
- Citrulline Malate Dose, Cycling? (T Nation forum, 2009)
- Arginine or Citrulline Malate? (T Nation forum, 2013)
- Citrulline Malate Storage (Exodus Strength forum, 2018)
- Citruline Malate Benefit? (T Nation forum, 2018)
- Citrulline malate (EliteFitness forums, 2020)
What forms of L-Citrulline are there?
| Form | What’s different | L-citrulline by weight | Per serving, on products we list |
|---|---|---|---|
| L-Citrulline (pure) | The amino acid on its own, so a weight on the label is all citrulline. | about 100.0 % | not in our price tables yet |
| Citrulline malate | The amino acid paired with malic acid; labels state a 2:1 or 1:1 ratio, or none at all. | about 56.6 to 72.3 % | 2.17 g |
What else is worth knowing about L-Citrulline?
- Where a label says citrulline malate, the number beside it is the weight of the whole compound, and only part of that is citrulline — about seven-tenths at the common 2:1 ratio. Where no ratio is given, the citrulline content cannot be read off the label.
- Trials of training performance mostly used six to eight grams of citrulline malate about an hour beforehand; trials of blood pressure used the plain amino acid, five to ten grams a day for one to eight weeks.
- A review of twelve trials in postmenopausal women recorded no side effects tied to citrulline, and reviews of the wider human research describe it as safe at the amounts used. Most trials ran eight weeks or less.
- Most training research is in young trained adults; most blood pressure work is in middle-aged and older adults, and several studies used watermelon rather than powder. Labels state the amount per serving, which may be more than one scoop.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (30 studies)
- Effects of Citrulline Malate Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-Analysis. (2026, meta-analysis)
- Effects of Citrulline Malate Supplementation on Muscle Strength in Resistance-Trained Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. (2022, meta-analysis)
- Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis. (2021, meta-analysis)
- Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis. (2019, meta-analysis)
- Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. (2017, randomised trial)
- Acute citrulline-malate supplementation improves maximal strength and anaerobic power in female, masters athletes tennis players. (2016, randomised trial)
- The effect of l-citrulline and watermelon juice supplementation on anaerobic and aerobic exercise performance. (2015, randomised trial)
- Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function in middle-aged and older adults: a systematic review and meta-analysis of randomized controlled trials. (2025, systematic review)
- Effects of Citrulline Supplementation on Exercise Performance in Humans: A Review of the Current Literature. (2020, systematic review)
- Effects of L-Citrulline Supplementation on Endothelial Function and Blood Pressure in Hypertensive Postmenopausal Women. (2022, randomised trial)
- Combined whole-body vibration training and l-citrulline supplementation improves pressure wave reflection in obese postmenopausal women. (2016, randomised trial)
- Impact of L-citrulline supplementation and whole-body vibration training on arterial stiffness and leg muscle function in obese postmenopausal women with high blood pressure. (2015, randomised trial)
- Short-term effects of L-citrulline supplementation on arterial stiffness in middle-aged men. (2012, randomised trial)
- Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis. (2020, meta-analysis)
- Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis. (2023, meta-analysis)
- Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis. (2022, meta-analysis)
- Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study. (2016, randomised trial)
- l-Citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. (2015, randomised trial)
- Citrulline supplementation in postmenopausal women: a systematic review of vascular, muscular, and metabolic effects. (2026, systematic review)
- Does l-citrulline supplementation and watermelon intake reduce blood pressure in middle-aged and older adults? A systematic review and meta-analysis of randomized controlled trials. (2025, meta-analysis)
- Effect of L-Citrulline Supplementation on Blood Pressure: a Systematic Review and Meta-Analysis of Clinical Trials. (2018, meta-analysis)
- The Effects of Combined Exercise with Citrulline Supplementation on Body Composition and Lower Limb Function of Overweight Older Adults: A Systematic Review and Meta-Analysis. (2023, meta-analysis)
- Effects of Citrulline alone or combined with exercise on muscle mass, muscle strength, and physical performance among older adults: a systematic review. (2020, systematic review)
- L-Citrulline Supplementation and Exercise in the Management of Sarcopenia. (2021, randomised trial)
- l-Citrulline Supplementation: Impact on Cardiometabolic Health. (2018, review)
- The Effects of Oral l-Arginine and l-Citrulline Supplementation on Blood Pressure. (2019, review)
- Citrulline in health and disease. Review on human studies. (2018, review)
- Influence of L-citrulline and watermelon supplementation on vascular function and exercise performance. (2017, review)
- Therapeutic Potential of Citrulline as an Arginine Supplement: A Clinical Pharmacology Review. (2020, review)
- Citrulline: from metabolism to therapeutic use. (2013, review)
How much does L-Citrulline cost?
That depends on the form and the pack, so we work out the price of the same dose of every L-Citrulline product we can find and rank them.