Citrulline: The "pump" of pre-workouts

What it is

Citrulline is an amino acid the body converts into arginine and, from there, into nitric oxide, a molecule that dilates vessels. It is sold as L-citrulline or citrulline malate, mainly in pre-workouts. It has no authorised EU health claims.

It is a popular and well tolerated supplement, but with two things worth knowing at the counter: the evidence on performance is modest, and it adds to other blood-pressure-lowering effects.

What is known

It increases the availability of arginine, from which nitric oxide is formed:

It dilates vessels slightly, hence the association with the "pump".
In studies, the effect on performance is small and variable.
It is usually well tolerated; effects are digestive and uncommon.

At the counter

When to recommend it

Adult who trains and wants to try it, never above the label dose
With a meal or split, to avoid digestive upset
Knowing that the effect is modest

When not to

Anyone on blood pressure medicines, nitrates or sildenafil without consulting their doctor
Pregnancy and breastfeeding: insufficient data
Under 18

What to say at the counter. Ask whether they take medication for blood pressure or the heart. It is one of the reasons to consult first. And as with most pre-workouts, check how many stimulants the product has besides citrulline.

Warnings

Important VESSEL-DILATING DRUGS (nitrates, sildenafil and similar) or ANTIHYPERTENSIVES: effects can add up and lower blood pressure too much; consult first.
Caution No authorised health claim: do not promise performance or a "pump".
Caution In pre-workouts it often comes with caffeine and other stimulants: add up the total.
Worth knowing At high doses it can cause digestive upset.

Pharmacokinetics

Absorption: Good by mouth, better than arginine directly.
Distribution: Spreads through tissues.
Metabolism: Converted into arginine in the kidney.
Elimination: In urine, after transformation.

Citrulline and arginine

Aspect	Citrulline	Arginine
Absorption	Good and sustained	Part is destroyed before reaching the blood
Effect on nitric oxide	Higher and steadier	Lower
Evidence	Modest	Even more limited
Key warning	Adds to antihypertensives and nitrates	The same

If one of the two is taken, citrulline is the better absorbed, but neither is a shortcut.

Self-assessment

Three questions. When you check your answers you will see the explanation for each one.

What should you ask someone requesting citrulline? Whether they take blood-pressure-lowering drugs or nitrates Their age only Whether they like the taste
Does it have an authorised EU health claim? Yes Only in sport No
How is its evidence on performance? Modest and variable Conclusive Always none

Training content. It does not replace the summary of product characteristics or clinical judgement.

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