Quick answer

L-arginine is an amino acid found in protein foods, and the body also makes its own; a normal diet supplies about 4 to 5 g a day. It is sold mostly for exercise, but NIH finds that 2 to 20 g a day has little to no effect on performance, so we make no benefit claim for it.^1,2

Key facts

The body uses arginine to build proteins and to make nitric oxide and creatine.¹
US adults take in about 4.4 g of arginine a day from food, on average.³
About 40% of the arginine you swallow is broken down in the gut before it reaches the blood.³
Up to 9 g a day for days or weeks is well tolerated in most studies, and safety beyond 3 months is unknown.¹

What L-arginine is

Arginine is one of the amino acids that proteins are built from. Healthy adults make some of their own, so it has traditionally not been counted as essential, and the rest comes from protein in food.³

Adults make arginine mainly in the kidneys, from citrulline produced in the small intestine.^1,3

Some arginine is converted to nitric oxide, a strong widener of blood vessels.¹

Arginine is one of three amino acids, with glycine and methionine, that the liver and kidneys use to make about 1 g of creatine a day.¹

In adults, about 40% of the arginine eaten is broken down in the small intestine before it reaches the bloodstream.³

That last point is one reason the arginine in a capsule does not simply add to the arginine in your blood, gram for gram.³

What the research shows

We make no benefit claim for arginine. Most supplements are sold for exercise, and that is where the research is clearest. Here is what it found.

NIH concludes that 2 to 20 g of arginine a day has little to no effect on performance in aerobic or anaerobic exercise, and that there is little scientific backing for its use to add strength, performance or recovery.^1,2

When well-trained athletes took arginine for 1 to 28 days, it typically had no effect on nitric oxide, blood flow, or exercise byproducts such as lactate and ammonia.¹

A 2016 systematic review of 62 studies in healthy adults aged 19 to 50 found that arginine gave little gain in athletic performance or recovery, and that most studies were small and prone to bias.⁴

Two pooled analyses reported gains. A 2020 analysis of 15 trials found better aerobic and anaerobic test results, but a 2025 comment showed calculation errors that inflated its estimates, which its authors acknowledged. A 2021 analysis of 11 small trials found a rise in VO2max, the most oxygen the body can use, so small that its confidence interval reached zero.^5,6,7,8

Studies of arginine by mouth disagree about growth hormone: extra arginine might lower it or raise it, and a rise might not lead to more blood flow to muscle or more protein building.¹

Little evidence shows that arginine on its own raises creatine in muscle, or that it matches or adds to taking creatine itself.¹

Most of the studies were small and mainly in men aged 18 to 25: only four of the 54 studies in one review included women.¹

Some trials looked at other outcomes this site does not cover.

How much people take

A nutritious diet supplies about 4 to 5 g of arginine a day.^1,2

Exercise studies have used 2 to 20 g of arginine a day, for up to 3 months.^1,2

In the 18 studies that compared arginine alone with a placebo, the most common amounts were 2 to 10 g a day taken as one dose, and up to 20 g a day split into three doses.¹

The dosage guide sets these amounts out in more detail, including a widely quoted protocol that has since been questioned.

Food sources

Arginine is found in many protein foods, especially animal foods and nuts. NIH names meat, poultry, fish, eggs, dairy products and legumes.^1,2

Watermelon is the best-known food source of citrulline, which the body turns into arginine: 1 cup of diced seedless watermelon has about 365 mg of citrulline.¹

The kidneys turn about 80% of the body's citrulline into arginine, and citrulline may raise blood arginine more efficiently than arginine itself, because more of it is absorbed from the gut.¹

What's in ours

What’s in ours

Ashwagandha Complex: L-Arginine, 300 mg per serving, from the label

Our Ashwagandha Complex lists 300 mg of L-arginine per serving. That is about one fifteenth of the 4.4 g an average US diet supplies, and far below the 2 to 20 g a day used in studies, so we make no claim for it.^1,3

Side effects, and who should ask first

At 9 to 30 g a day, the most commonly reported side effects are stomach and gut discomfort, such as diarrhea and nausea.^1,2

Arginine can lower blood pressure. NIH notes a slight drop at 9 to 30 g a day, and a 2022 pooled analysis of 22 trials found systolic pressure about 6.4 mmHg and diastolic pressure about 2.6 mmHg lower than with placebo, with the systolic drop seen from about 4 g a day.^1,9

In a 2006 trial, 153 people who had just had a first heart attack took 3 g of arginine three times a day or a placebo for 6 months, alongside standard care. Arginine did not change the heart and blood vessel measures studied, 6 people taking it died against none on placebo, and the safety committee stopped enrollment.¹⁰

No official upper limit is set for arginine. NIH says most studies suggest that up to 9 g a day for several days or weeks is safe and well tolerated, and that the safety of high doses beyond 3 months is not known.¹

Do not take arginine if you have recently had a heart attack¹⁰
Ask your doctor first if you take medicine for blood pressure or your heart, or if your blood pressure runs low⁹
Ask first if you have kidney disease or reduced kidney function¹¹
Ask first if you are pregnant or nursing, or under 18

The official sources we use do not name a specific medicine that interacts with arginine. That is not proof of safety: arginine can lower blood pressure, so ask your doctor or pharmacist before combining it with medicines that do the same.^1,9

Questions people ask

Does L-arginine increase nitric oxide?

Some arginine is turned into nitric oxide in the body. But in studies where trained athletes took arginine for up to four weeks, it typically did not change nitric oxide levels or blood flow.¹

Is L-arginine good for bodybuilding?

The research says probably not. NIH concludes it has little to no effect on strength or performance at 2 to 20 g a day, and a 2016 review of 62 studies came to the same view.^1,4

Does L-arginine raise growth hormone?

Given into a vein at 30 g, it often does in people whose pituitary gland works normally, which is why hospitals use it as a test. Taken by mouth, studies conflict: it may raise or lower growth hormone, and a rise may not mean more muscle protein.^1,11

Is L-citrulline better than L-arginine?

More citrulline is absorbed from the gut, and the kidneys turn about 80% of it into arginine, so it may raise blood arginine more efficiently. NIH finds little evidence that either one helps exercise performance.¹

Is L-arginine safe for the heart?

Not after a heart attack: in a 2006 trial, 6 people taking arginine died against none on placebo, and the researchers advised against it. It can also lower blood pressure, so ask your doctor first if you have a heart condition or take heart or blood pressure medicine.^9,10

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Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.