L-lysine is an essential amino acid, and PubMed lists 3,806 records on it as a supplement or nutrient. Only 9 of them are trials on cold sores, and the newest is from 1987.
This page maps what lysine does, what those trials found, and where label claims run ahead of them.
Quick Answer: What Is L-Lysine Good For?
Lysine is an amino acid your body cannot make. As a supplement it is bought mainly for cold sores, where the trials split by dose: 1,000 to 1,200 mg a day mostly failed, and 3,000 mg helped in 1 trial of 52 people. A 2015 Cochrane review found no evidence it prevents them.
Key Takeaways
- PubMed holds 3,806 lysine supplement or nutrient records, but 9 herpes trials.
- The newest placebo-controlled lysine trial for cold sores dates from 1987.
- Trials at 1,000 to 1,200 mg a day mostly found no benefit.
- One 1987 trial of 3,000 mg daily averaged 2.4 fewer outbreaks.
- A 2015 Cochrane review found no evidence lysine prevents cold sores.
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What Lysine Is
Lysine is 1 of the 9 essential amino acids. Your body cannot build it, so every gram comes from food or a supplement.
- Form in supplements: L-lysine, usually as the hydrochloride salt.
- Main food sources: Dairy, fish, meat, eggs and legumes.
- Low sources: Cereals such as wheat and rice.
- Adult requirement: About 30 mg per kg of body weight a day.
The 30 mg figure is the current recommendation, and a 2024 study suggested older women may need more.[1]Dietary Lysine Requirements of Older Adults Stratified by Age and Sex — Journal of Nutrition (2024) View source For a 70 kg adult it is about 2,100 mg a day, which most diets exceed. Which foods carry the most lysine is a question with real numbers behind it.
The Size of the Evidence
Most of what PubMed calls lysine is biochemistry, not supplements. The counts make the difference visible.
| What PubMed holds on lysine | Count |
|---|---|
| Records with lysine in the title or abstract | 92,630 |
| Records on lysine as a supplement or nutrient | 3,806 |
| Of those, tagged as human | 732 |
| Of those, animal with no human tag | 1,273 |
| Of those, tagged as clinical trials | 86 |
| Records pairing lysine with herpes | 212 |
| Herpes records tagged as trials (newest 1987) | 9 |
| Systematic reviews on lysine and herpes | 1 |
Of 9 herpes records tagged as trials, 1 tested a poly-lysine gel rather than oral lysine. The newest oral trial against placebo was published in 1987.
Cold Sores: Why Most People Buy It
A 1997 review noted that most pharmaceutical-grade lysine hydrochloride is sold to suppress recurrent herpes.[2]The metabolic roles, pharmacology, and toxicology of lysine — Journal of the American College of Nutrition (1997) View source The record behind that use is short, and what the 8 cold sore trials found splits cleanly by dose.
- Negative: 3 trials at 1,000 to 1,200 mg a day.
- Positive: 1,248 mg of the salt plus a diet change, in 41 people.
- Most positive: 3,000 mg a day for 6 months, in 52 people.
- Healing time: Shortened in only 1 trial.
The 2015 Cochrane review found no evidence of efficacy for lysine in preventing cold sores.[3]Interventions for prevention of herpes simplex labialis (cold sores on the lips) — Cochrane Database of Systematic Reviews (2015) View source A 2023 dermatology review read the same trials as effective for prevention.[4]Diet in Dermatology: Review of Diet's Influence on Rosacea, Hidradenitis Suppurativa, Herpes Labialis, and Vitiligo — American Journal of Lifestyle Medicine (2023) View source
The Arginine Idea
The theory behind lysine for herpes came from cell cultures. In 1964, herpes virus failed to replicate in cells deprived of arginine.[5]Amino acid requirements of herpes simplex virus in human cells — Journal of Bacteriology (1964) View source
- In cells: Lysine partly inhibited virus growth.
- In people: 0 trials tested a low-arginine diet on its own.
- In real diets: Most people already eat more lysine than arginine.
- Practical upshot: The ratio is a hypothesis, not a measured effect.
What It Is Reasonable to Expect
Stated plainly, a 1,000 mg capsule adds about 12% to the roughly 8 g of lysine a typical diet already supplies.
- Reasonable: A measured top-up of an essential amino acid.
- Reasonable to try: Cold sore prevention, at trial doses, with your doctor.
- Not established: Healing a sore that has already appeared.
- Not established: Bone, skin or weight benefits.
On those terms a 1000 mg lysine capsule is a simple way to take it, and 3 capsules come close to the dose of the most positive trial.
Calcium and Bone
This is the least known use, and the evidence is 1 short 1992 paper.
- Calcium load test: 400 mg of lysine blunted urine calcium loss in healthy women.
- Absorption: 800 mg a day raised calcium absorption in 45 patients.
- Bone density: Not measured.
- Fractures: 0 trials.
The 1992 study compared lysine with valine and tryptophan, and only lysine raised absorption.[6]Dietary L-lysine and calcium metabolism in humans — Nutrition (1992) View source It suggests a mechanism, not a bone treatment.
Anxiety and Stress
Three human trials reported calmer stress responses. Two of them gave lysine together with an equal dose of arginine.
- Syria, 2004: Lysine-fortified wheat for families on cereal diets.
- 2005: 3 g lysine plus 3 g arginine for 10 days.
- Japan, 2007: 2.64 g of each for 1 week, in 108 adults.
- Lysine alone, well-fed adults: Barely tested.
The 2007 trial found lower trait and state anxiety and lower basal cortisol in men.[7]Oral treatment with L-lysine and L-arginine reduces anxiety and basal cortisol levels in healthy humans — Biomedical Research (2007) View source
Safety in Brief
At the doses people take, lysine has a clean record. A 2019 review of 71 studies found mainly stomach symptoms.[8]Safety assessment of L-lysine oral intake: a systematic review — Amino Acids (2019) View source
- Common: Nausea, stomach ache or diarrhea.
- Provisional ceiling: 6,000 mg a day, from that review.
- Rare: 1 published case of kidney damage, in 1996.
- Untested: Pregnancy, breastfeeding and kidney disease.
Who should be careful, and why, is covered in the kidney and calcium cautions.
Speak to a Clinician Before Taking Lysine If
- You have kidney disease, or have ever been told your kidney function is reduced
- You are pregnant or breastfeeding; we found 0 trials of lysine supplements in pregnancy
- You take high-dose calcium, or an aminoglycoside antibiotic such as gentamicin
- Your cold sores are frequent, severe, near the eye, or you are immunocompromised
- You have gallbladder or heart disease, which one review flags as a theoretical concern
Frequently Asked Questions
What happens if you take L-lysine every day? +
In trials lasting up to 1,095 days, the main problems were stomach symptoms, and they were no more common than on placebo. Whether it prevents anything depends on dose and goal.
What is the downside of L-lysine? +
Mainly that its best-known use is unproven: a 2015 Cochrane review found no evidence it prevents cold sores. Stomach upset and 1 published kidney case are the safety notes.
Does lysine help with belly fat? +
We found 0 controlled trials showing that lysine reduces belly fat or body weight in people.
Does lysine help sagging skin? +
We found 0 controlled trials of oral lysine for sagging skin. Collagen contains lysine, but 1 g a day adds about 12% to what most diets supply.
Is lysine an essential amino acid? +
Yes. It is 1 of 9 essential amino acids, so the body cannot make it and must get it from food or supplements.
What is lysine used for most? +
Cold sores. A 1997 review noted that most pharmaceutical-grade lysine hydrochloride is sold to suppress recurrent herpes simplex.
Does lysine help calcium absorption? +
In 1 short 1992 study of 45 people with osteoporosis, 800 mg a day raised calcium absorption. 0 trials have measured bone density or fractures.
Is lysine good for anxiety? +
Possibly, with a catch. 2 of the 3 supplement trials gave lysine with an equal dose of arginine, so lysine alone is barely tested.
How many studies are there on lysine? +
PubMed holds 92,630 records mentioning lysine, mostly biochemistry. 3,806 concern it as a nutrient or supplement, and 86 of those are tagged as trials.
Can lysine cure herpes? +
No. WHO states herpes medicines can shorten outbreaks but cannot cure the infection, and 0 lysine trials reported a cure.
Related Reading
- Lysine vs Arginine: Does the Ratio Matter?
- How Much Lysine to Take Per Day
- Lysine for Anxiety: Three Trials, One Catch
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