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L-Arginine Benefits, Side Effects & Safety Information

Published: 13th May 2018. Last updated: 21th July 2019.

Shaun Ward MSc ANutr

Staff Writer


L-Arginine is one of 9 essential amino acids that are found in the diet.

Arginine plays an important role in removing ammonia from the body, immune function, cell division, wound healing, and the release of hormones.

However, its most interesting role is as a precursor for the synthesis of nitric oxide, which is a molecule that regulates blood pressure by helping blood vessels to relax and expand.

For this reason, it is now popular to use l-arginine supplementation in an attempt to directly produce more nitric oxide and gain athletic advantages (oxygen and blood flow).

The Potential Benefits of L-Arginine

Below we have listed everything we believe could be viewed as a potential benefit, based on credible scientific studies:

May Increase Blood Flow

Arginine may help to increase blood flow by directly producing more nitric oxide through a process called the L-arginine-NO pathway [1].

This is where arginine acts as a substrate for nitric oxide synthase enzymes to produce nitric oxide, which then signals for a cascade of reactions that ultimately lead to vascular relaxation and blood vessel dilation.

However, improved blood flow from l-arginine supplementation only seems to occur in people with high blood pressure [2] [3].

In healthy individuals, significant differences in blood flow are rarely apparent from l-arginine supplementation [4] [5].

The reason why l-arginine does not appear to have a pronounced effect on nitric oxide production (a small increase at best) and blood flow in healthy individuals is in part due to the poor absorption of l-arginine from the intestines before it can have an appreciable impact on the body.

This is evidenced by a 30 gram infusion of arginine effectively reducing blood pressure and peripheral resistance in healthy individuals, yet an oral dose failed to replicate such effects [6].

As the effects are larger in those with high blood pressure, it is theorized that the body can upregulate the intestinal absorption of l-arginine under certain conditions, although this is yet to be validated.

The Problem With L-Arginine

Intestinal uptake of arginine supplementation under normal conditions tends to be very poor, and has only shown to improve during various diseases that affect cardiovascular health [7].

At low doses the absorption of arginine is appreciable [8], but with gradually higher oral doses that are necessary to have a physiological effect, the rate of absorption dramatically reduces [9].

The intestinal stage of absorption appears to be a key regulatory step. This may be due to a limited availability of cationic amino acid transporters that are responsible for transporting arginine across the intestinal barrier.

In fact, some researchers even propose that increasing the level of blood or intracellular arginine levels is not important for nitric oxide production anyway, with arginine availability not typically being a limiting factor for the production of nitric oxide.

As such, an excess of arginine, achieved through supplementation, is not a good method to yield higher levels of nitric oxide.

Better ways to get l-arginine to systemic tissue is not by consuming l-arginine directly, but actually via supplemental l-ornithine or l-citrulline.

How to Take L-Arginine?

There is not a standard recommended dose of l-arginine to improve cardiovascular health or athletic performance.

However, the standard pre-exercise dose tends to around 3-6 grams, with limited side effects noted at such a dose.

L-Arginine Safety And Side Effects

The vast majority of evidence suggests that l-arginine supplementation is generally safe and well-tolerated by most men

However, some side effects can occur such as:

  • Increased risk of bleeding
  • Reduced glycemic control
  • Low blood pressure
  • Potassium imbalances

In addition, high doses such as those above 10 grams per day can result in gastrointestinal distress and diarrhea [4].


L-Arginine is one of the 9 essential amino acids that are found in the diet, and is necessary for a great number of metabolic reactions and processes.

Although its use is very popular in athletic populations to enhance blood flow and improve athletic performance, the supplement is unable to achieve this effect due to its poor intestinal absorption.

Its only potential benefit appears to only be for people with high blood pressure, as the body may be able to upregulate its absorption under severe health conditions.

3-6 grams per day is the recommended dose that is shown to be safe.

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