If muscle pump is one of the things you look for in a pre-workout, there is a good chance you've seen L-citrulline somewhere on the ingredient label.
It has become one of the most common ingredients used in modern pre-workout supplements, particularly formulas designed around pump and training performance.
But what actually is L-citrulline?
Does it directly increase nitric oxide? Is citrulline malate the same thing? Does taking more automatically produce a bigger pump? And, most importantly, what does the research actually show?
L-citrulline has considerably more science behind it than many fashionable pre-workout ingredients, but that doesn't mean every claim made about it is supported.
Here's what you need to know.
What Is L-Citrulline?
L-citrulline is a naturally occurring amino acid.
Unlike essential amino acids, your body can produce citrulline itself. It is also naturally present in certain foods, with watermelon being one of the best-known dietary sources.
Its relevance to sports nutrition comes primarily from what happens to L-citrulline after it enters the body.
Rather than being used primarily for building muscle protein, citrulline participates in the body's urea cycle and can be converted into another amino acid called L-arginine.
That relationship is important because arginine is involved in the body's production of nitric oxide.
And that's where the connection with pre-workout supplements begins.
L-Citrulline, Arginine and Nitric Oxide
The process can be simplified like this:
L-Citrulline → L-Arginine → Nitric Oxide
After citrulline is absorbed, much of it travels to the kidneys where it can be converted into arginine.
Arginine can then act as a substrate for nitric oxide synthesis.
Nitric oxide is a signalling molecule involved in the regulation of blood vessels.
This is the reason you'll frequently see L-citrulline included in pump and performance-focused supplements.
It isn't a stimulant.
It doesn't work like caffeine.
And you aren't supposed to experience the beta-alanine-style tingling sensation from it.
Its interest within pre-workout formulation primarily revolves around the arginine–nitric oxide pathway.
Why Take Citrulline Instead of Arginine?
This creates an obvious question.
If arginine is used to produce nitric oxide, why not simply take arginine?
Interestingly, consuming L-citrulline can be an effective way of increasing circulating arginine availability.
Oral arginine undergoes substantial metabolism before reaching systemic circulation, whereas citrulline follows a different metabolic route and can subsequently be converted into arginine.
This is one reason L-citrulline has become such a common ingredient in modern pre-workouts.
You'll still find arginine in certain products, sometimes alongside citrulline, but citrulline has become particularly popular in pump-oriented formulations.
Does L-Citrulline Give You a Better Muscle Pump?
This is where marketing and research need separating.
What creates a muscle pump?
During resistance training, repeated muscular contractions increase blood flow to the working muscles.
Fluid also moves into and around muscle tissue.
The result is the temporary swollen, full appearance lifters know as a muscle pump.
Because citrulline can increase circulating arginine and is connected with nitric-oxide production, it has become heavily associated with pump supplements.
However, that doesn't mean scientists have conclusively demonstrated that every dose of L-citrulline will produce a dramatically larger muscle pump in every lifter.
Reviews of resistance-exercise research have found that although citrulline reliably influences circulating citrulline and arginine, evidence for measurable increases in muscle blood flow and muscular swelling during resistance training is less consistent.
So there is an important distinction:
There is a strong physiological reason why citrulline is used in pump formulas, but the size of the pump you experience will depend on far more than one ingredient.
Your workout structure, repetitions, rest periods, hydration, carbohydrate intake, sodium intake and individual physiology can all influence how pumped you feel.
Does L-Citrulline Improve Training Performance?
Researchers have investigated both L-citrulline and citrulline malate for several forms of exercise.
The results are interesting, but not completely straightforward.
A systematic review and meta-analysis looking at high-intensity strength and power exercise found a small overall effect in favour of citrulline supplementation.
Another meta-analysis looking specifically at citrulline malate before resistance training found a small increase in the number of repetitions performed compared with placebo.
However, not every study produces a positive result.
More recent research evaluating citrulline malate across different types of exercise continues to describe the overall effect as small and context-dependent.
That's important.
Citrulline isn't a magic powder that suddenly adds 20kg to your bench press.
Where benefits have been detected, they tend to be relatively modest.
For somebody interested in sports nutrition, that makes citrulline an interesting ingredient.
For somebody expecting a dramatic overnight transformation, the evidence doesn't support that expectation.
L-Citrulline and Resistance Training
Citrulline is particularly popular among people training for bodybuilding and hypertrophy.
Why?
Because bodybuilding sessions commonly involve:
Multiple sets
Moderate-to-high repetitions
Repeated muscular contractions
Relatively short recovery periods
A deliberate focus on muscle pump
High training volume
These are very different demands from performing one maximal single repetition.
Research into citrulline and resistance training has therefore frequently examined repetition performance and muscular endurance, rather than simply asking whether citrulline makes somebody instantly stronger.
Some studies and meta-analyses have observed small improvements in repetition performance.
Others haven't.
The most accurate interpretation is that citrulline may influence certain types of high-intensity or repeated exercise performance, but results vary according to the exercise, dose, supplement used and individual.
L-Citrulline and Endurance Exercise
This is another area where exaggerated supplement claims should be treated carefully.
If nitric oxide is involved with blood-vessel regulation, it is easy to assume that citrulline must automatically improve endurance.
The research doesn't support such a simple conclusion.
Systematic reviews examining aerobic and endurance exercise have generally failed to show a clear significant improvement from acute citrulline supplementation.
That doesn't make L-citrulline useless.
It simply demonstrates why an ingredient shouldn't be given benefits that haven't been consistently shown in research.
Resistance training, sprint-style exercise and prolonged endurance exercise are different physiological challenges.
A result observed during one type of exercise should not automatically be applied to every other sport.
L-Citrulline vs Citrulline Malate: What's the Difference?
This is one of the most important things to understand when reading a pre-workout label.
You will normally encounter one of two names:
L-Citrulline
This is the standalone amino acid.
If a supplement states:
6g L-Citrulline
the ingredient amount refers to L-citrulline itself.
Citrulline Malate
Citrulline malate combines citrulline with malate, derived from malic acid.
This means:
8g citrulline malate does not necessarily equal 8g L-citrulline.
That distinction is frequently missed when people compare pre-workouts.
The amount of actual citrulline depends on the ratio used in the ingredient.
For example, you may see citrulline malate described using ratios such as 2:1.
That's one reason comparing nothing except the headline number on the front of a tub can be misleading.
Check what form of citrulline the manufacturer is actually using.
Is Citrulline Malate Better Than Pure L-Citrulline?
There isn't currently enough evidence to say that citrulline malate is universally superior to L-citrulline.
A complication in the research is that different studies have used different forms, doses and citrulline-to-malate ratios.
That makes direct comparisons difficult.
Malate itself participates in energy metabolism, which is one reason the combination became popular in sports supplements.
However, when you're comparing two products, don't automatically assume that a larger citrulline-malate number means you're receiving more actual L-citrulline.
Read the label rather than the marketing headline.
If you'd like to understand how pump formulas differ from stimulant and performance formulas, our guide to the different types of pre-workout explains the differences in more detail.
How Much L-Citrulline Has Been Studied?
Research protocols vary considerably, which makes declaring one universal "perfect dose" misleading.
Studies involving pure L-citrulline have examined several different amounts and supplementation periods.
Research involving citrulline malate has commonly tested amounts around 6–8g before exercise, while research using pure L-citrulline has used different protocols.
These are descriptions of amounts investigated by researchers—not instructions to exceed the serving size of a commercial product.
Always follow the manufacturer's directions for the product you're using.
And remember:
6g L-citrulline and 6g citrulline malate aren't necessarily equivalent.
That distinction matters when comparing ingredient panels.
A Real Pre-Workout Example: Dark Labs Crack OG
To see how citrulline fits into an actual multi-ingredient formula, look at Dark Labs Crack OG.
The current manufacturer formulation lists 4,000mg of L-citrulline per scoop, alongside beta-alanine, agmatine, arginine and several stimulant ingredients.
That's a useful example of why analysing a pre-workout requires looking at the whole formula.
The citrulline is only one component.
Crack OG is primarily a high-stimulant pre-workout, so its overall effects cannot simply be attributed to L-citrulline.
Likewise, comparing it with a stimulant-free pump formula purely on the amount of citrulline would ignore everything else present in each product.
Formulas can also change, so always check the current product label before purchasing or using a supplement.
Is L-Citrulline a Stimulant?
No.
L-citrulline isn't a stimulant.
It doesn't act like caffeine and doesn't belong in the same ingredient category.
That means L-citrulline can be used in both:
Stimulant pre-workouts
and
Stimulant-free pump formulas.
This is one reason somebody who trains late at night might choose a pump-oriented product containing citrulline without necessarily wanting a large dose of caffeine.
You can compare different approaches in our Pump & Performance collection.
L-Citrulline vs Caffeine
Although they're frequently contained in the same pre-workout, they serve completely different purposes.
Caffeine
Caffeine is a central nervous system stimulant.
Its effects can include increased alertness and reduced perception of fatigue, and it has a substantial body of exercise-performance research behind it.
L-Citrulline
L-citrulline isn't stimulating.
It is primarily included because of its conversion to arginine and relationship with nitric-oxide pathways.
Someone shouldn't therefore judge citrulline by asking:
"Can I feel it kicking in?"
You might clearly notice 300mg of caffeine.
You won't necessarily experience a distinctive sensation from L-citrulline.
That doesn't tell you how much is present.
L-Citrulline vs Beta-Alanine
These ingredients are also frequently found together, but again they have very different functions.
Beta-Alanine
Beta-alanine is used by the body to produce carnosine within skeletal muscle.
Research into beta-alanine focuses particularly on repeated high-intensity exercise and muscular buffering.
Beta-alanine can also produce the familiar tingling sensation known as paraesthesia.
L-Citrulline
L-citrulline is associated instead with the arginine–nitric oxide pathway.
No beta-alanine-style tingles are required.
A product containing both ingredients isn't using two versions of the same thing.
They're included for completely different reasons.
Does L-Citrulline Build Muscle?
This is another distinction worth making.
L-citrulline isn't protein powder.
It isn't an anabolic drug.
And taking citrulline doesn't directly create new muscle tissue simply because your muscles look fuller during a workout.
The muscle pump is temporary.
Long-term muscle growth is primarily driven by factors including:
Progressive resistance training
Appropriate training volume
Sufficient dietary protein
Adequate energy intake
Recovery
Sleep
Consistency over time
A stronger pump shouldn't therefore be confused with permanent muscle growth.
Research has investigated potential relationships between citrulline supplementation, exercise and body composition, but the evidence doesn't justify treating citrulline as a muscle-building shortcut.
Does a Bigger Pump Mean a Better Workout?
Not necessarily.
A pump can feel fantastic.
It can also provide useful feedback during hypertrophy-style training because you're clearly loading and contracting a particular muscle.
But pump alone isn't a measurement of muscle growth.
You could have an enormous arm pump from repeatedly curling a very light weight without providing the progressive overload required for long-term development.
Likewise, an effective low-repetition strength session may produce less pump while still providing a powerful training stimulus.
So enjoy the pump.
Just don't mistake it for the entire purpose of training.
What Should You Look For in a Citrulline Pre-Workout?
When browsing pre-workout supplements, don't simply look for the word "citrulline".
Look deeper.
1. Check Which Form Is Used
Is it:
L-citrulline
or
citrulline malate?
They're not identical.
2. Check the Actual Amount
Does the manufacturer disclose how much you're getting per serving?
Transparent labels make comparing formulas much easier.
3. Look at Serving Size
A product might advertise a large ingredient panel, but the total scoop size still needs to accommodate everything listed.
4. Examine the Rest of the Formula
Look for ingredients such as:
Beta-alanine
Caffeine
Betaine
Taurine
Tyrosine
Nitrates
Glycerol
Electrolytes
The effectiveness and overall experience of a pre-workout depends on the complete formulation—not one fashionable ingredient.
5. Check the Stimulant Content
A pump-focused ingredient doesn't automatically mean the product is stimulant-free.
Some of the strongest stimulant pre-workouts available also contain L-citrulline.
Always check caffeine and stimulant quantities separately.
Can You Take Citrulline Without Caffeine?
Yes.
Citrulline itself doesn't require caffeine.
That's why it's frequently found in stimulant-free pump products.
For somebody who:
trains in the evening
is sensitive to caffeine
already consumes plenty of caffeine
wants a break from stimulants
primarily wants a pump-oriented formula
a stim-free formula may make more sense than automatically choosing a heavily caffeinated pre-workout.
As we explain in our Types of Pre-Workout guide, the strongest stimulant product isn't automatically the best product for every training session.
Does More L-Citrulline Mean a Better Pre-Workout?
Not automatically.
An impressive amount of one ingredient doesn't compensate for a poorly designed overall formula.
And a product containing fewer total ingredients isn't necessarily inferior either.
When comparing products, consider:
Form + dose + complete formula + intended purpose.
A stimulant-free pump formula and an aggressive high-stimulant pre-workout may both contain citrulline while being designed to create completely different training experiences.
That's why comparing pre-workouts based on one ingredient alone rarely tells the whole story.
Frequently Asked Questions About L-Citrulline
- What does L-citrulline do in pre-workout?
L-citrulline can increase circulating arginine availability. Arginine is involved in nitric-oxide production, which is why citrulline commonly appears in supplements formulated around pump and exercise performance.
- Is L-citrulline a stimulant?
No. L-citrulline isn't a stimulant and doesn't work in the same way as caffeine.
- Does L-citrulline contain caffeine?
No. Pure L-citrulline doesn't contain caffeine. However, many pre-workout products combine citrulline with caffeine, so always check the complete ingredient panel.
- What's the difference between L-citrulline and citrulline malate?
L-citrulline is the standalone amino acid. Citrulline malate combines citrulline with malate, meaning the total weight of citrulline malate isn't necessarily the same as the amount of actual citrulline.
- Does L-citrulline cause tingles?
L-citrulline isn't normally responsible for the characteristic pre-workout tingles. That sensation is most commonly associated with beta-alanine.
- Does L-citrulline increase nitric oxide?
L-citrulline can increase circulating arginine, which is a substrate used in nitric-oxide synthesis. This relationship is one of the principal reasons citrulline is studied and included in sports supplements.
- Is L-citrulline good for muscle pumps?
Citrulline is commonly included in pump formulas because of its relationship with arginine and nitric-oxide pathways. However, studies directly measuring resistance-exercise blood flow and muscle swelling have produced mixed results, so a dramatic pump shouldn't be guaranteed solely because a product contains citrulline.
- Does L-citrulline make you stronger?
Research has found small improvements in certain high-intensity and repetition-based exercise measures, but results aren't consistent across every study. Citrulline shouldn't be viewed as something that automatically increases maximal strength.
- When is L-citrulline normally taken?
Many studies examining acute exercise performance have provided citrulline or citrulline malate before exercise. Commercial formulations differ, so follow the timing and serving instructions supplied by the manufacturer.
The Bottom Line
L-citrulline has become one of the defining ingredients of modern pump-focused pre-workout supplements.
And unlike many ingredients that appear briefly in sports-nutrition trends before disappearing again, citrulline has been investigated across a substantial body of research.
The science gives us a fairly clear explanation of the underlying pathway:
L-citrulline can increase arginine availability, and arginine is involved in nitric-oxide production.
What becomes less certain is translating that mechanism into claims that everyone will experience dramatically larger pumps, greater strength or better performance.
Research into resistance and high-intensity exercise has found some small positive effects.
Research into endurance performance is less convincing.
And direct evidence surrounding blood flow and muscle swelling during resistance exercise remains mixed.
That's exactly why we think understanding an ingredient is more useful than simply believing the claims on the front of a tub.
When comparing a citrulline-containing pre-workout, ask:
Which form is being used?
How much is disclosed?
What else is in the formula?
Is it primarily a pump, stimulant or all-round performance product?
Those questions will tell you considerably more than simply buying whichever tub promises the "craziest pump".
Browse our full pre-workout range, explore Pump & Performance supplements, or read our guide to the different types of pre-workout to understand which type of formula best matches the way you train.
Research Behind This Guide
This guide was informed by peer-reviewed research including systematic reviews and meta-analyses investigating L-citrulline and citrulline malate in resistance exercise, strength and power performance, aerobic exercise and perceived exertion.
Research includes:
Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis
Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis
Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis
Effects of Citrulline Malate Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-Analysis
Research findings continue to evolve and individual studies use different products, doses, populations and exercise protocols.
Important Information
Food supplements should not be used as a substitute for a varied, balanced diet and healthy lifestyle.
Always check the current ingredient label and follow the manufacturer's recommended serving instructions. Formulations can change without notice.
If you are pregnant or breastfeeding, taking medication, have a medical condition or are unsure whether a supplement is suitable for you, seek appropriate professional advice before use.
