Citrulline

What is citrulline used for?

Citrulline is a non-essential amino acid: your body can produce it, and it is naturally found in watermelon, from which it derives its name (Citrullus). Its interest in sports nutrition lies in a somewhat counter-intuitive metabolic detour.

To increase the production of nitric oxide — the molecule that dilates blood vessels and increases blood flow to the muscle — arginine is needed. However, orally administered arginine is largely destroyed in passage by an intestinal and hepatic enzyme, arginase. Citrulline, on the other hand, escapes this filter: it passes through, reaches the kidney, and is converted there into arginine. The paradoxical yet well-established result: taking citrulline increases blood arginine more than taking arginine itself.

This is why it has largely replaced L-arginine in serious pre-workout formulas.

Citrulline or citrulline malate: what's the difference?

L-citrulline is the pure molecule. Citrulline malate is this same molecule combined with malic acid, an intermediate of the Krebs cycle involved in aerobic energy production.

The distinction matters for dosage. Citrulline malate is generally presented in a 2:1 ratio, meaning two parts citrulline to one part malate. A tub stating "8 g of citrulline malate" therefore delivers only about 5.3 g of actual citrulline. Some brands play on this ambiguity.

In practice: if you are only aiming for vasodilation, pure L-citrulline is clearer and often cheaper at an equal dose. If you are also looking for endurance during long sessions, malate adds an argument, even if its specific benefit is less documented than that of citrulline.

What dosage is effective?

This is where most products on the market fall short.

• Pure L-citrulline: 3 to 6 g per serving. Below 3 g, the effect becomes difficult to distinguish.
• Citrulline malate 2:1: 6 to 8 g per serving, which equates to 4 to 5.3 g of effective citrulline.

Take it 30 to 60 minutes before your workout, with water. This is the time required for renal conversion to arginine. Unlike beta-alanine or creatine, citrulline does not need to be accumulated over several weeks: it acts upon intake. Some studies, however, suggest an additional benefit after a week of daily intake.

A useful reflex when faced with a ready-made booster: look for the citrulline line in the nutrition facts table. If it's buried in an undisclosed "blend," or if it shows 1 to 2 g, the dose is cosmetic. This is precisely why many users buy their citrulline separately and supplement a light pre-workout.

What effects can actually be expected?

Three things are reasonably documented in sports nutrition literature:

Pump. This is the most immediately noticeable effect: a feeling of swollen muscles and visible veins during the session, linked to increased blood flow. It's a sensation, not a performance measure, but it is very real.

Training volume. Several studies report an increase in the number of repetitions performed in the last sets, where fatigue sets in. The effect is modest, on the order of a few extra repetitions over an entire session.

Soreness. A reduction in muscle pain at 24 and 48 hours has been observed in several protocols using citrulline malate.

What not to expect from it: citrulline does not build muscle mass on its own, does not replace adequate protein intake, and does not compensate for poor sleep. It is a workout aid, not a driver of progress.

A note of honesty: a significant portion of research on citrulline concerns vascular function in a medical context, not the gym. This work cannot be translated into commercial claims, and no health claims are authorized in Europe for citrulline to date. For any health-related questions, consult a doctor.

Citrulline: Is there any danger?

Citrulline is well tolerated at usual doses. Unlike arginine, it causes few digestive issues, even at high doses — this is one of its practical advantages.

Real points of vigilance:

• Vasodilator treatments: citrulline acts on the same pathway as some medications (nitrates, hypertension treatments, PDE5 inhibitors). The combination can cause a drop in blood pressure. Medical advice is essential.
• Kidney or liver failure: conversion occurs in the kidney, and the urea cycle is involved. Do not use without supervision.
• Pregnancy and breastfeeding: insufficient data, abstinence recommended.
• Herpes: citrulline increases arginine, which is suspected to promote outbreaks in affected individuals. The subject is debated but worth knowing.

As with any food supplement, French regulations require not exceeding recommended doses and remind that a supplement does not replace a varied diet.

Frequently Asked Questions

What is citrulline?

A non-essential amino acid — the body can produce it — first isolated in watermelon, hence its name, derived from the Latin Citrullus. It is not involved in protein composition: its role is metabolic. Converted into arginine by the kidney, it fuels the production of nitric oxide, the molecule that dilates blood vessels. As a supplement, it is found in two forms: pure L-citrulline and citrulline malate, combined with malic acid, usually in a 2:1 ratio.

How does citrulline work?

Through a detour, and that's what makes it so interesting. Directly ingested arginine is largely destroyed by arginase, an enzyme abundant in the intestine and liver: little reaches circulation. Citrulline, however, is not a substrate for this enzyme: it passes intact, reaches the kidney, and is converted there into arginine — bypassing the obstacle. This arginine then fuels NO-synthase, which produces nitric oxide, which relaxes blood vessel walls and increases blood flow to the muscle. Hence the pump felt during training. Allow 30 to 60 minutes for this chain to take effect.

What are the benefits of citrulline?

Let's start with the framework: no health claims are authorized in Europe for citrulline, so no one is allowed to promise you a health benefit. What is reasonably documented in sports nutrition comes down to three points. Pump, the most immediately noticeable effect. Training volume: a few extra repetitions in the last sets, a real but modest effect. Soreness, reduced at 24 and 48 hours in several protocols using citrulline malate. Nothing more: it does not build muscle, does not replace protein, and does not compensate for a bad night's sleep.

When should citrulline be taken?

Thirty to sixty minutes before your workout, with water, on an empty or light stomach. This delay corresponds to the time it takes for citrulline to be converted into arginine by the kidney, and then for nitric oxide levels to rise; taken five minutes before warming up, it will not have had time to act. On non-training days, it does not provide much benefit, as its effect is linked to exertion: it's better to reserve doses for workout sessions. However, some protocols suggest a slight additional benefit after a week of daily intake, which may justify a fixed morning dose as a supplement.

What is the daily dosage of citrulline?

Three to six grams of pure L-citrulline per serving, or six to eight grams of 2:1 ratio citrulline malate, which corresponds to 4 to 5.3 g of effective citrulline. A single dose per day, before training, is sufficient. Below 3 g of actual citrulline, the effect becomes difficult to distinguish, and this is exactly the dosage found in most ready-made boosters. There's no need to go above 8 g: the benefit no longer increases, and the cost per session climbs unnecessarily.

How to use citrulline malate?

Dilute 6 to 8 g in 300 to 400 ml of water, 30 to 60 minutes before your workout. Two practical precautions. First, the ratio: check that it is stated (2:1 most often) and do the calculation, because 8 g of citrulline malate only represents about 5.3 g of actual citrulline. Then the taste: malic acid is frankly acidic, almost astringent, and many give up the product for this reason. Mix it with a flavored drink, with EAAs, or with a little sugar-free syrup rather than pure water. It combines easily with beta-alanine, electrolytes, and creatine in the same shaker.

What is the best citrulline?

The one whose label allows you to calculate the real dose. Specifically: pure L-citrulline if you want a clear dosage and the best value per gram, or citrulline malate clearly stated in a 2:1 ratio if you are also looking for the added benefit of malic acid. Beware of "citrulline malate" mentions without a specified ratio. Powder is preferable to capsules for an arithmetic reason: reaching 6g in capsules requires swallowing about ten of them.

Citrulline or arginine?

Citrulline, in almost all cases. At an equal oral dose, it raises plasma arginine more than arginine itself, and it is better tolerated digestively.

When to take arginine and citrulline together?

If you wish to use both, take them at the same time, 45 to 60 minutes before your session: this is the longer of the two delays, for arginine. But frankly, the combination offers little. Both feed into exactly the same pathway — that of nitric oxide — and citrulline achieves this better orally. Adding arginine on top mostly means paying twice for the same mechanism, with the added risk of digestive issues specific to arginine. If you want to supplement your citrulline, do so with ingredients that act differently: beta-alanine, creatine, electrolytes.

Which fruit contains citrulline?

Watermelon, by far the leader: citrulline was first isolated from it and owes its name to it. It's found in the flesh, but the concentration is higher in the white part between the red flesh and the rind, the part everyone throws away. Melon, cucumber, and squash also contain it, in much smaller quantities. The problem is arithmetic: reaching 3g of citrulline would require about a kilogram of watermelon, a volume and sugar load incompatible with pre-workout intake.

What are the side effects of citrulline?

It's one of the best-tolerated ingredients on the market: unlike arginine, it causes few digestive issues, even at 6 or 8g. Reported discomforts are rare and mild — temporary abdominal discomfort, sometimes a slight drop in blood pressure in individuals already hypotensive. Real precautions concern four situations: vasodilator and antihypertensive treatments, including nitrates and PDE5 inhibitors, with which the combination can cause a drop in blood pressure; kidney or liver failure; pregnancy and breastfeeding, due to lack of data; and recurrent herpes outbreaks, as citrulline increases arginine. In each of these cases, seek medical advice beforehand.

Is citrulline bad for the kidneys?

In a person with normal kidney function, there is no indication of a problem at usual doses: the kidney is where citrulline is converted to arginine, which does not mean it is stressed. The situation changes in cases of known kidney or liver failure, or a urea cycle disorder: citrulline should then be avoided without supervision. The same caution applies if you are on blood pressure medication. This page does not replace medical advice: in case of doubt or pathology, consult your doctor before supplementing.

Does citrulline have an effect on erection?

The question comes up often, and the honest answer is: we are not allowed to claim it, and we do not sell this product for that purpose. No health claims are authorized in Europe for citrulline, on this subject or others. What does exist is research conducted in a medical setting on vascular function, which cannot be translated into a commercial promise or a self-administered dosage. The useful reminder: an erectile dysfunction is a symptom, sometimes the first visible sign of a cardiovascular or metabolic problem. It requires a medical consultation, not a supplement bought online — especially since citrulline interacts precisely with the treatments concerned.

Citrulline and sleep: can it be taken in the evening?

Yes. Citrulline is not a stimulant: it does not act on the central nervous system or on alertness, unlike caffeine. Taking it late in the day before a late session does not disrupt sleep, making it one of the few pre-workout ingredients compatible with evening training. This is also the basis of stimulant-free formulas. The real point of vigilance is the product in which it is incorporated: if your booster also contains 300 mg of caffeine, it is the latter that will cause problems. In this case, see our caffeine-free boosters.

Can it be combined with creatine?

Yes, without any problem: the two do not use the same pathways and do not compete with each other. Creatine can be taken anytime during the day, citrulline before your workout.

Our Selection

We prioritize references that clearly display the ratio and dosage per serving, particularly from IO.Genix, Now Foods, and Nutriting. To create a complete workout routine, also check out our boosters, beta-alanine, and electrolytes.

At our store in Vendargues, ten minutes from Montpellier, we can help you calculate the actual citrulline dose contained in the booster you already use — often a first surprise.

To learn more: muscle pump, what it is and how to get it.