What Does L-Citrulline Do In Pre-Workout? Dietitian Explains

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If you’ve seen L-Citrulline listed as an ingredient in your pre-workout, you’re probably wondering what it is and does. As a dietitian, I’ll explain the benefits of having L-citrulline before a workout, the recommended dosage, and potential side effects.

Key Takeaways

  • L-Citrulline supplementation increases arginine levels and nitric oxide, which improves blood flow to your muscles and creates a “pump” feeling while lifting weights.
  • Studies show that 6 grams of L-Citrulline 30 minutes before exercise is an effective dose. L-Citrulline may be labeled as “L-Citrulline” or “Citrulline Malate,” which are slightly different forms (explained below).
  • L-Citrulline can be taken independently (i.e., bought in bulk from a place like Bulk Supplements) or mixed with other pre-workout ingredients in a clinically-dosed formula (such as Transparent Labs).

What Is L-Citrulline?

L-Citrulline is an amino acid your body can make on its own.

It plays an essential role in the body, one of which is in the urea cycle, which removes harmful substances like ammonia from your body through urine. 

It also assists in widening blood vessels, which can be beneficial during exercise.

Although your body produces L-citrulline independently, you can boost your levels by eating citrulline-rich foods or taking supplements.

How Does L-Citrulline Work?

L-Citrulline is involved in amino acid breakdown.

It primarily works by making your blood vessels wider, known as vasodilation.

Vasodilation increases blood flow and is linked with various benefits, including lower blood pressure and improved exercise performance.

The mechanism behind vasodilation with L-Citrulline supplementation is that some of it gets converted into another amino acid called arginine. Arginine then becomes nitric oxide, which relaxes the muscles in your blood vessels, making them wider.

Arginine then becomes nitric oxide, which relaxes the muscles in your blood vessels, making them wider. 

Research shows some nuances between arginine and citrulline metabolism (the way they are broken down and absorbed).

More specifically, citrulline seems more easily absorbed in the bloodstream than arginine. 

As such, if you consume more L-Citrulline, it might:

Citrulline Malate vs L-Citrulline

Now that you know how citrulline works, it’s worth discussing its other form, citrulline malate.

Citrulline malate combines L-Citrulline with malic acid. Malic acid (L-Malate) is important for energy production.

As such, citrulline malate might be better for strength training because it may give you extra energy (e.g., increasing the number of repetitions in your workouts).

L-citrulline might be better for endurance training because it may help your muscles use oxygen more efficiently (e.g. running for longer before getting tired). 

Some manufacturers often use low-quality citrulline malate containing a lower ratio of citrulline:malate (e.g., 1:2). Low-quality options rarely disclose the citrulline:malate ratio on the label.

An optimal ratio would be 2:1 in a dose of 8g citrulline malate. For example, you should get 5.3g of L-citrulline and 2.7g of malic acid, totaling the effective dose of 8g of citrulline malate.

Having said this, much of the evidence on the specific role of malate combined with citrulline in sports is inconclusive and inconsistent.

Benefits of L-Citrulline

the benefits of l-citrulline for exercise performance

The following benefits for exercise performance have been seen both with L-Citrulline (endurance) and citrulline malate (strength training):

Delays Fatigue in Endurance Workouts

Evidence indicates that a single dose of citrulline might not boost endurance right away, but taking it for a week or more can lead to better endurance by increasing oxygen content in the muscles. 

It won’t make your body take in more oxygen, but it can help your muscles become more efficient with oxygen usage when you exercise, delaying acid buildup (H+) and fatigue.

For example, a study with cyclists found that those who took 6g per day of L-Citrulline (for seven days) could ride longer before getting tired (about 12% longer) and had more power in their legs when cycling. 

This research suggests that citrulline supplements might improve endurance workouts by delaying fatigue; however, more research is needed.

Enhances Muscle Endurance During Strength Training

Evidence suggests that a single dose of citrulline malate taken before a gym workout can boost performance by increasing the number of repetitions performed for each exercise.

In a study with 14 resistance-trained men, participants could do more reps for upper body exercises (chin ups, push ups)  when they had 8g of citrulline malate. 

Results from another study showed that 12 resistance-trained males who ingested 8g citrulline malate could perform a higher number of repetitions while performing lower body exercises (on the leg press, hack squat, and leg extension machines).

So, citrulline malate supplements (with adequate citrulline:malate ratio) might improve your gym workouts.

Are There Any Side Effects of L-Citrulline?

are there any side effects of l-citrulline in pre workout

Evidence suggests that L-Citrulline supplementation seems safe, even if taken at high doses. However, there appears to be an upper limit of effectiveness as the body can only use a limited amount.

For example, one study examined how the body processes citrulline at different doses. 

Researchers gave citrulline to eight healthy men in 2, 5, 10, or 15 grams and then checked their blood for other amino acids and hormones. 

Results showed that even at high doses, citrulline didn’t cause any side effects (e.g., stomach upset).

However, they did find that:

  • It increases the levels of some amino acids in the blood, like arginine, which is crucial for making nitric oxide and increasing levels in the blood (aiding vasodilation).
  • At high doses (15 grams), arginine levels didn’t rise much, possibly because the body cannot convert all of the citrulline to arginine.

How To Properly Use L-Citrulline In Your Pre-Workout Routine

L-citrulline can be bought separately and added to your pre-workout supplement or found in pre-workout supplements in different doses.

However, doses of L-citrulline in multi-ingredient pre-workout supplements are generally far lower than those that have shown performance improvement.

The most commonly used doses in research are 8 grams per day of citrulline malate (for resistance training) and 6 grams per day of L-Citrulline (for endurance training). 

Based on research, the most common times to take it are 30-60 minutes before a strength workout or daily for a minimum of 7 days for endurance performance effects.

Here’s an example of how to use L-Citrulline, assuming you are an 80kg (176 pounds) active person aiming to improve strength performance:

  • Use 8g citrulline malate (based on a 2:1 ratio), which equates to approximately 5.3 grams of citrulline and 2.7 grams of malate.
  • Add it to a DIY pre-workout (e.g., with caffeine and beta-alanine mix), and consume it ~ 30 minutes before a workout.
  • If you prefer not to have a multi-ingredient pre-workout supplement, have it alone with water, preferably on an empty stomach, to promote better absorption.

Pre-Workouts That Have A Clinical Dose of L-Citrulline

As mentioned, L-Citrulline can be taken as part of a pre-workout supplement or added to one.

As such, below are some product recommendations that might help you choose what best suits you:

Transparent Labs Bulk Pre-Workout

Transparent Labs Bulk

Transparent Labs’ Bulk Pre Workout Supplement is a multi-ingredient pre-workout that provides an appropriate dose of citrulline malate. 

With one scoop, you can get 8 grams of citrulline malate 2:1, which falls in line with the doses used in research. 

BulkSupplements L-Citrulline Powder

Bulk Supplements L-Citrulline

BulkSupplements offers L-Citrulline Powder for those who prefer a single-ingredient supplement.

You can use this powder alone or combine it with other pre-workout ingredients to make your own pre-workout.

This L-citrulline powder provides 3 grams of L-citrulline per serving, so you would need two servings to get the effective dose of 6 grams.

Myths and Misconceptions About L-Citrulline

The most common myth is that L-citrulline is better than citrulline malate.

This myth is based on L-Citrulline containing 100% pure citrulline and citrulline malate being a blend with less of the active ingredient. 

However, evidence suggests that because both contain the active ingredient L-Citrulline, they produce similar results (assuming a 2:1 ratio).

If anything, citrulline malate may produce better results because malate increases the absorption of L-citrulline and increases energy production (similar to the role of creatine).

What Is L-Citrulline Usually Combined With?

L-Citrulline can be consumed with water on an empty stomach and still benefits performance.

However, L-Citrulline is often combined with the following ingredients in pre-workouts:

Beta-Alanine, Creatine, BCAA’s, & L-Tyrosine

One study, including 6g citrulline malate, beta-alanine, caffeine, creatine, BCAAs, and L-Tyrosine, showed that ingesting this multi-ingredient supplement may increase strength performance.

Another study shows that 1.5g of L-Citrulline combined with a pre-workout supplement containing caffeine, creatine, β-alanine, BCAAs, and B vitamins improves leg press strength and is safe when consumed continuously for 28 days.

BCAAs and Choline (A-GPC From The B Vitamin Group)

This supplement combo may be helpful for endurance athletes.

One recent study (2023) tested 8 g BCAAs, 6 g l-citrulline, and 300 mg alpha-glyceryl phosphorylcholine over seven days on trained cyclists. 

Researchers found that this supplement mix improved peak power in a 20 km cycling test and increased endurance in high-intensity cycling (boosting peak power by 11% and extending the time cyclists could keep going by 36.2%). 

What Are Natural Sources of L-Citrulline?

While not all foods have been checked for L-Citrulline, it is known to exist in larger quantities in one particular food: Watermelon.

“Watermelon is the most significant, natural plant source of L-citrulline”

MDPI Journal

1000 grams of watermelon flesh (the red, juicy part) corresponds to around 2 g L-Citrulline, so you would need to eat a lot of watermelon to get 6 grams (the dose used in research studies).

Other foods containing far less citrulline (between 6 and 41 times less than watermelon, according to one study) include pumpkins, cucumber, cantaloupe melon, and squash.

Although the body makes citrulline, some people supplement their diet because more L-Citrulline might boost health and performance.

Frequently Asked Questions

Do You Have To Cycle L-Citrulline?

L-Citrulline is considered safe for daily use, and there is no research to suggest that citrulline needs to be cycled to exert benefits in athletes. 

Does L-Citrulline Expire?

Yes, it can expire, so reading the expiry date on the packaging is essential.

Expired L-citrulline might not work as well, but it’s not usually harmful. Avoid keeping it in the heat and humidity to prevent it from degrading more quickly.

Can You Take L-Citrulline Every Day?

Yes, you can.

Research has shown that citrulline appears more effective when taken long-term rather than now and then. L-Citrulline has been tested at higher doses (e.g., 15 grams) and has no side effects. 

Does Citrulline Burn Fat?

Citrulline does not burn fat.

It is an amino acid that might improve muscle endurance by boosting nitric oxide (and thus blood flow in muscles), potentially delaying fatigue during exercise. If you want to burn fat, you must be in a calorie deficit for some time.

Learn About Other Ingredients


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About The Author

Giulia Rossetto

Giulia Rossetto is a qualified Dietitian and Nutritionist. She holds a Masters in Human Nutrition (University of Sheffield, UK) and more recently graduated as a Dietitian (University of Malta). Giulia aims to translate evidence-based science to the public through teaching and writing content. She has worked 4+ years in clinical settings and has also published articles in academic journals. She is into running, swimming and weight lifting, and enjoys spending time in the mountains (she has a soft spot for hiking and skiing in the Italian Dolomites).

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