L-Lysine vs L-Arginine Compared

Quick answer

Lysine is an essential amino acid the body cannot make, needed at about 2.1 g a day for a 70 kg adult. Arginine the body makes itself, and NIH found that 2 to 20 g a day has little to no effect on exercise performance. Both come mostly from protein foods, and neither has an official upper limit.^1,2,3

Key facts

Lysine is one of nine essential amino acids that must come from food, while arginine is made in the kidneys from citrulline.^2,4
Fewer than 1% of US adults eat less than the average lysine requirement, and US adults average 4.4 g of arginine a day from food.^5,6
Lysine has a moderate grade for its protein role and early grades for calcium, stress and strength, while arginine has no graded benefit.^1,2,7,8
Neither has an official upper limit: up to 9 g a day of arginine for days or weeks is described as well tolerated, and a provisional figure for lysine is 6,000 mg a day.^2,3
Arginine carries cautions for people on medicines for the heart or blood vessels, while the lysine record includes one case report of serious kidney damage.^9,10,11

What each one is

Some arginine is converted to nitric oxide, a strong widener of blood vessels.²

Lysine is the amino acid most likely to run short in diets based on cereals, especially wheat.^1,12

Both are amino acids, the building blocks of protein, which is where the likeness ends. Lysine is a nutrient with a fixed requirement that has to be met from protein foods. Arginine is partly made by the body, partly eaten, and partly turned into other compounds such as nitric oxide and creatine.^2,12

How the evidence grades compare

The grades are lopsided. Lysine has one moderate claim, which is a nutrient role, and three early ones that rest on one or two small studies each. Arginine has none, because the larger reviews found little to back it.^1,13

Provides lysine, an essential amino acid the body uses to build protein*^1,4,5,12

Moderate evidence

A well-established nutrient function. Lysine is one of nine essential amino acids that must come from the diet for the body to keep building protein, as NIH and a 2020 review of lysine metabolism describe. An expert panel for WHO, FAO and UNU puts the adult requirement at about 30 mg per kg of body weight a day. In US survey data, fewer than 1% of adults fall below the average requirement, so for most people food already covers it and extra lysine adds little.

Amount studied: Requirement: about 30 mg per kg of body weight a day from all food, or about 2.1 g for a 70 kg adult

May help the body absorb and hold on to calcium*⁷

Early evidence

One small study from 1992. When 30 women took a large calcium dose, adding 400 mg of lysine blunted the rise in calcium lost in urine in the 15 healthy women. In a second part, 45 people under medical care absorbed more calcium while taking 800 mg of lysine a day than while taking two other amino acids. We found no larger or longer trial.

Amount studied: 400 mg with a single calcium dose, or 800 mg a day for a short period

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.¹³

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.²

Where each one comes from

A review of arginine nutrition lists seafood, nuts, seeds, meats, algae, watermelon juice, and rice and soy protein concentrates among foods relatively high in arginine, and notes that the milk of most mammals, including cows, is relatively low.⁶

Lysine comes mainly from animal foods such as meat, fish, eggs and dairy. In one lab analysis, lysine made up about 7% of animal proteins but about 3.6% of plant protein isolates on average.^14,15

Animal proteins and legumes such as soy supply more lysine than the requirement pattern, while cereals supply only 57% to 86% of it, and cassava and yam just over 90%.¹

The practical consequence is about which diets are thin. Lysine runs short first in diets built on cereals, so someone who eats mainly wheat and little animal protein is the person most likely to fall short. No source we read names a group likely to fall short of arginine.^1,6

The research record

What the research looks like for each^{2,3,7,8,13,14,16}
	L-arginine	L-lysine
Size of the review base	54 studies in the review NIH cites; 62 in a 2016 expert review	71 human studies in a 2019 review
Who was studied	Mostly men aged 18 to 25; four of the 54 studies included women	Mostly small trials; one in pregnant women measured the requirement
Longest use	None of the 54 lasted 3 months or longer	Up to 3 years
Known weak spots	A 2020 pooled analysis was later shown to have calculation errors	Every claim except the protein role rests on one or two small studies

Forms you will see

FDA's rule on amino acids added to food allows L-lysine as the free amino acid or as a hydrochloride salt, and caps total lysine at 6.4% of a food's protein.¹⁷

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.²

Arginine hydrochloride is also a prescription injection: in hospital, 30 g is infused into a vein over 30 minutes to test how much growth hormone the pituitary gland can release.¹⁸

Who might pick which

Lysine suits a person whose diet is built on cereals with little meat, fish, eggs or dairy, since that is where the requirement is hardest to meet. The requirement also rises in pregnancy, from about 37 mg per kg early on to about 50 mg per kg late.^1,14
Arginine has no group the sources say it is for. NIH finds little scientific backing for using it to add strength, performance or recovery, and most of the studies were small.^2,13
For most people who eat enough protein, neither supplement adds much, and a protein food is the simpler source of both.^5,6

What's in ours

What’s in ours

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

What’s in ours

Immune Support: L-Lysine, 100 mg per serving, from the label

Safety differences

The safety of high-dose arginine taken for more than 3 months is not known.²

The label of the arginine injection used in hospitals asks doctors to consider the nitrogen load arginine adds in people with reduced kidney function.¹⁸

The side effects reported in human studies were mainly nausea, stomach ache and diarrhea. Pooled across studies, these were no more common with lysine than without it.³

Arginine: ask first if you take medicine for blood pressure or your heart, and do not use it after a recent heart attack.^2,10
Lysine: ask first if you have kidney disease. The one serious report we found is a single case of kidney damage in a woman taking lysine, and it does not show cause.¹¹
Both: ask first if you are pregnant or nursing, or under 18.

Questions people ask

Which is better, L-lysine or L-arginine?

Neither is shown to be better, since they do different jobs. Lysine's strongest claim is a moderate-graded role as an essential amino acid, while arginine has no graded benefit because NIH found little to no effect on exercise performance at 2 to 20 g a day.^1,2

Is L-arginine or L-lysine an essential amino acid?

Lysine is. NIH lists it among the nine essential amino acids that people must get from food. Arginine is not on that list, because adults make it in the kidneys from citrulline, although they also eat about 4.4 g a day.^2,4,6

Can you get enough of both from food?

Most people can. In US survey data fewer than 1% of adults ate less than the average requirement for any essential amino acid, lysine included, and arginine intake averaged 4.4 g a day. Meat, fish, eggs, dairy and legumes supply both.^5,6

Which has more side effects?

Arginine does at larger amounts. At 9 to 30 g a day the commonly reported effects are stomach and gut discomfort, and it can lower blood pressure. In 71 human studies of lysine, nausea and stomach ache were not more common than without it, though a single case of kidney damage has been reported.^2,3,11

See what we make

Every product shows its whole label and what its lab report covers. The store opens soon.

See the Full Measure line Ashwagandha Complex Immune Support

Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

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