Quick answer

L-lysine is an essential amino acid: your body uses it to build protein but cannot make it, so it has to come from food. Adults need about 30 mg per kg of body weight a day, roughly 2.1 g at 70 kg, and fewer than 1% of US adults fall short. Evidence for taking extra is early.^1,2,3

Key facts

Lysine made up about 7% of animal proteins but about 3.6% of plant protein isolates in one lab analysis.⁴
Cereals such as wheat supply only 57% to 86% of the lysine the requirement pattern calls for.²
No official upper limit exists; a 2019 review of 71 studies proposed 6,000 mg a day as a provisional level without adverse effects.⁵
The EU's list of permitted health claims has no claim for lysine.⁶

What lysine is

Lysine is one of the nine essential amino acids, with histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan and valine, that people must get from food.¹

Protein in food is broken down into amino acids, and the body uses them to assemble its own proteins. Lysine is one of the nine it cannot make for itself, so protein building depends on a steady supply from meals.^1,7

Lysine the body does not use is broken down, mainly in the liver.⁷

Lysine is the amino acid most likely to run short in diets based on cereals, especially wheat.^2,7

That last point explains much of the research on lysine. Several of the human studies were done in places where wheat or other grains supply most of the protein, such as communities in Syria and India.^2,8,9

What the evidence shows

Four claims are graded below. The first, that lysine is an essential nutrient, rests on firm ground. The other three each rest on one or two small trials, and each shows the amount that was tested.

Provides lysine, an essential amino acid the body uses to build protein*^1,2,3,7

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*¹⁰

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

Taken with arginine, may ease feelings of stress*^8,11

Early evidence

Two trials, both run by a company that makes lysine. In 108 healthy Japanese adults, 2.64 g of lysine plus 2.64 g of arginine a day for a week lowered scores on standard questionnaires about tension and worry, and lowered the stress hormone cortisol in men, compared with placebo. In a three-month trial in Syrian communities whose diet relied on wheat, lysine-fortified flour lowered the cortisol response to a blood draw in women and a measure of everyday worry in men. One tested a combination and the other involved people whose diets were low in lysine, so neither shows what lysine alone does for people who eat enough protein.

Amount studied: 2.64 g of lysine with 2.64 g of arginine a day for one week, or lysine-fortified wheat flour for three months

May slightly increase muscle strength at very high intakes*⁹

Early evidence

One small trial. Forty young men in India, some of them undernourished, ate controlled diets for 8 weeks that supplied either their usual lysine intake (about 25 to 40 mg per kg of body weight a day) or 80 mg per kg. The high-lysine diet raised muscle strength by about 7.5% but did not change muscle mass or the other measures. Some of the men usually ate less lysine than the requirement, and the study was read as an abstract only.

Amount studied: 80 mg per kg of body weight a day from a controlled diet for 8 weeks, about 5.6 g for a 70 kg man

Some research on lysine looked at outcomes this site does not cover. The safety section below covers one review that included lysine.

How much you need

An expert panel for WHO, FAO and UNU puts the adult requirement at about 30 mg of lysine per kg of body weight a day, about 2.1 g for a 70 kg adult. Its safe level of intake is about 24% higher, near 37 mg per kg.²

In US national survey data from 2001 to 2018, fewer than 1% of adults ate less than the average requirement for any essential amino acid, lysine included.³

For most people, then, food already covers the requirement, and a supplement adds to an intake that is already enough. The dosage page has the figures by body weight and for pregnancy.³

Where lysine comes from

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.^4,12

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%.²

People who eat little or no animal food can still get enough by including legumes such as soy, which carry more lysine than grains do.²

Forms on the label

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.¹³

Supplement labels usually name L-lysine or L-lysine hydrochloride (HCl). We found no human research showing that one of these forms does more than the other.

What's in ours

What’s in ours

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

The 100 mg in the product above is about 5% of the daily requirement of a 70 kg adult, and well below the amounts tested in the trials above. We make no lysine claim for it.²

Side effects and who should ask first

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.⁵

No official upper limit is set for lysine. A 2019 systematic review of 71 human studies proposed a provisional no-observed-adverse-effect level of 6,000 mg a day, based on gut symptoms.⁵

A 1996 case report described a 44-year-old woman who developed Fanconi syndrome and tubulointerstitial nephritis, serious kidney damage that progressed to chronic kidney failure, in association with taking lysine. It is a single case.¹⁴

A Cochrane review of 32 trials of ways to prevent cold sores included lysine and found no evidence that it prevents them, and this site makes no claim that it does. If cold sores keep coming back, talk to a doctor: in the same review, long-term antiviral medicines did reduce recurrences, though the benefit was small.^14,15

Ask your doctor first if you have kidney disease or reduced kidney function
Ask first if you are pregnant or breastfeeding, or under 18
Ask your pharmacist if you take a prescription medicine; the official drug labels we checked do not address lysine either way^16,17

Questions people ask

What does l-lysine do for men?

The same as for women: it is an essential amino acid used to build protein. One small trial in young men found a slight strength gain at very high intakes, graded early above, and we found nothing else specific to men.^1,9

Is l-lysine good for your skin?

A PubMed search found no human trials of lysine supplements for skin, so this page makes no skin claim.

Do vegans need a lysine supplement?

Usually not, if the diet includes legumes such as soy, lentils or beans. Plant protein isolates carry about half the lysine of animal proteins on average, and cereals are the shortest, so a diet built mostly on grains is the one to watch.^2,4

What is the best form of l-lysine?

Labels list L-lysine or L-lysine hydrochloride, and FDA allows either form to be added to food. We found no human research favoring one, so compare the amount of lysine per serving instead.¹³

See what we make

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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.