Arginine or citrulline?

Citrulline, if the goal is the nitric oxide pathway. Citrulline is converted into arginine inside the body and raises blood arginine better than taking arginine directly, and it sits better too. Oral arginine loses a good part along the way.

Does arginine help with the muscle pump?

That is the promise, resting on a reasonable logical chain, but the data are inconsistent: the aerobic effect in the meta-analysis comes with huge heterogeneity and the anaerobic one is small. In highly trained people the specific review finds no benefit.

Does arginine raise growth hormone?

Given intravenously it is used precisely as a clinical test to stimulate growth hormone, which is where the selling point comes from. Transferring that to an oral capsule and turning it into more muscle is a leap the performance evidence does not back.

How much arginine do you need?

Acute protocols use 0.15 g per kilo, about 10 g for a 70 kg person, taken an hour to an hour and a half before. Almost no pre-workout on the market contains that amount.

Home / Arginine / Guide

Arginine · Weak evidence

What arginine is for and what the evidence says

The short answer. Arginine is sold as a nitric oxide precursor: more nitric oxide, more vasodilation, more blood to the muscle. The chain holds on paper and is weak in practice. A meta-analysis finds improvements, but with huge scatter between studies on the aerobic side, and the review on nitric oxide related supplements notes an awkward pattern: where an effect is seen is in untrained or moderately trained people, and in highly trained subjects it does not appear. On top of that, a good part of the arginine swallowed never reaches the blood.

Reviews find no consistent effect. It is listed because it sells, not because it works. No figure on this page is attributed to a specific product: the effect belongs to the ingredient and every number carries its source next to it.

01 What it does and how much

Each row is a measured effect, with the figure the study gives and the source number. Where the evidence gives no figure, the column says so instead of making up a percentage.

Effects of arginine with their source
Effect	How much	Detail
Aerobic performance	SMD 0.84	The meta-analysis rates it as a large effect, but with 89 % heterogeneity, which is the technical way of saying the studies are not alike and the average summarises poorly what happened in each. [1]
Anaerobic performance	SMD 0.24	A small effect, this time with zero heterogeneity: the studies agree the effect is small. It is the more reliable of the two figures and the less flashy. [1]
In highly trained athletes	no effect	The review on nitric oxide donors says it directly: benefits are seen in untrained or moderately trained people, and when highly trained people are supplemented no improvement appears. Exactly the opposite of who marketing sells it to. [2]
Acute dose in the protocols	0.15 g/kg	60 to 90 minutes before the effort. For 70 kg that is about 10.5 g in one serving, far more than most pre-workouts contain. [1]
Chronic dose in the protocols	1.5-2 g/day	For 4 to 7 weeks on the aerobic side; for the anaerobic side the protocols go up to 10-12 g a day for 8 weeks. Amounts and timelines almost nobody sustains. [1]

02 How to take it

Dose. 0.15 g per kilo in a single serving, or 1.5-2 g a day for several weeks, which is what the studies use.
When. The acute serving, 60 to 90 minutes before the effort.
How long before you notice it. The acute regime acts in the same session; the chronic regimes were trialled for 4 to 8 weeks.

Details that change the result

Citrulline is now used more than arginine for the same purpose, for a specific reason: it raises blood arginine better than oral arginine itself. If the goal is nitric oxide, citrulline is the better-supported route.
At high doses arginine easily causes digestive problems. That is one of the practical reasons for the switch to citrulline.
A pre-workout with 1 g of arginine is nothing like the 10 g in the studies. It is a label ingredient more than a dose.
None of this is a safety problem: the problem is that the measured effect does not hold up once the person taking it trains seriously.

03 When it makes sense and when it does not

Worth it if

Starting out in training, the profile where studies do see improvements.
As part of a formula that already includes it, without paying for it as a star ingredient.

Not worth it if

With a high training level: it is exactly the group where the review finds no effect.
Looking for a gym pump: for that, citrulline has better evidence and better absorption.
At the small doses in a typical pre-workout, which come nowhere near those in the studies.

04 Sources

Every figure above comes from here. They are position stands from scientific societies, meta-analyses and peer-reviewed reviews: if a claim cannot hang from one of these lines, it is not on the page. References are cited in their original form.

Viribay A, Burgos J, Fernandez-Landa J, Seco-Calvo J, Mielgo-Ayuso J. Effects of Arginine Supplementation on Athletic Performance Based on Energy Metabolism: A Systematic Review and Meta-Analysis. Nutrients. 2020;12(5):1300. Quince estudios en el metaanalisis: DME 0,84 (IC 95 % 0,12-1,56; I2 89 %) en pruebas aerobicas y DME 0,24 (IC 95 % 0,05-0,43; I2 0 %) en anaerobicas; protocolos de 0,15 g/kg entre 60 y 90 minutos antes. doi:10.3390/nu12051300
Bescos R, Sureda A, Tur JA, Pons A. The Effect of Nitric-Oxide-Related Supplements on Human Performance. Sports Med. 2012;42(2):99-117. En sujetos no entrenados o moderadamente entrenados los donantes de oxido nitrico mejoran la tolerancia al ejercicio; en sujetos muy entrenados no se observa mejora del rendimiento. doi:10.2165/11596860-000000000-00000

This is not medical advice. It is what some studies say about an ingredient, not a protocol for you. With an illness, medication or pregnancy involved, the decision belongs to a healthcare professional who knows you.

Questions about arginine

Answered with the data on this page

Arginine or citrulline?: Citrulline, if the goal is the nitric oxide pathway. Citrulline is converted into arginine inside the body and raises blood arginine better than taking arginine directly, and it sits better too. Oral arginine loses a good part along the way.
Does arginine help with the muscle pump?: That is the promise, resting on a reasonable logical chain, but the data are inconsistent: the aerobic effect in the meta-analysis comes with huge heterogeneity and the anaerobic one is small. In highly trained people the specific review finds no benefit.
Does arginine raise growth hormone?: Given intravenously it is used precisely as a clinical test to stimulate growth hormone, which is where the selling point comes from. Transferring that to an oral capsule and turning it into more muscle is a leap the performance evidence does not back.
How much arginine do you need?: Acute protocols use 0.15 g per kilo, about 10 g for a 70 kg person, taken an hour to an hour and a half before. Almost no pre-workout on the market contains that amount.

And now, which to buy

Prices, kept apart from the evidence

This page explains what arginine does and deliberately names no brand. The comparison is the other half: 10 products from 3 stores from €23.50 per kg, sorted by price and by how verifiable their certification is.

See the arginine comparison

Other guides

What each supplement does, with its sources