A 2019 review of 71 lysine studies found mainly stomach symptoms, and no more of them than on placebo. The real cautions sit outside those trials.
Kidney disease, pregnancy, high-dose calcium and certain antibiotics were never tested in people, and that is where caution belongs.
Quick Answer: What Are the Side Effects of Lysine?
Mostly mild stomach symptoms: nausea, stomach ache and diarrhea. A 2019 review of 71 studies found them no more often than on control, and proposed 6,000 mg a day as a provisional no-adverse-effect level. One 1996 case linked lysine to kidney damage. Kidney disease, pregnancy and high-dose calcium remain untested.
Key Takeaways
- A 2019 review pooled 71 studies with doses up to 17,500 mg.
- Stomach symptoms were the main effect, with a risk ratio of 1.02.
- 1 published case linked lysine to kidney damage that became chronic.
- In rats, lysine worsened kidney injury from the antibiotic gentamicin in 1984.
- We found 0 randomized trials of lysine supplements in pregnancy.
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What the Safety Reviews Found
Two systematic reviews from the same group pooled every human lysine study they could find, for any of what lysine is good for.
- Studies: 71, with 3,357 participants.
- Doses: 16.8 mg to 17,500 mg a day.
- Duration: 1 to 1,095 days.
- Main effects: Nausea, stomach ache and diarrhea.
Pooled, the risk of stomach symptoms was no higher than control, a risk ratio of 1.02.[1]Safety assessment of L-lysine oral intake: a systematic review — Amino Acids (2019) View source The 2020 version set the provisional no-adverse-effect level at 6.0 g a day.[2]Comprehensive Safety Assessment of L-Lysine Supplementation from Clinical Studies: A Systematic Review — Journal of Nutrition (2020) View source
The Kidney Question
The kidney record is thin rather than reassuring, and most of it comes from animals.
- In people: 1 case of Fanconi syndrome and kidney inflammation, 1996.
- Outcome: Progression to chronic kidney failure.
- In rats: 600 mg per rat over 4 hours caused acute kidney failure.
- In kidney disease: 0 trials of lysine supplements.
The case involved a 44-year-old woman taking lysine from a health food store.[3]Fanconi's syndrome and tubulointerstitial nephritis in association with L-lysine ingestion — American Journal of Kidney Diseases (1996) View source In the rat work, lower doses of lysine produced no significant kidney changes.[4]Effects of lysine and other amino acids on kidney structure and function in the rat — American Journal of Pathology (1985) View source
Calcium: More Absorbed, Less Lost
Lysine changes calcium handling, which matters if you already take a lot of calcium.
- Absorption: 800 mg a day raised it in 45 osteoporotic patients.
- Urine: 400 mg blunted calcium loss after a 3 g load, in healthy women.
- Harm: None reported, but the combination was not studied long term.
- Kidney stones: 0 studies linking lysine supplements to stones.
Those 1992 results came from 2 short studies.[5]Dietary L-lysine and calcium metabolism in humans — Nutrition (1992) View source
Where Cold Sore Doses Sit
Most people take lysine for the cold sore evidence, and those doses sit well under the pooled ceiling.
- Failed trials: About 800 to 1,000 mg of lysine a day.
- Most positive trial: 3,000 mg a day for 6 months.
- Provisional ceiling: 6,000 mg a day.
- Gap: Even the high trial dose is half that ceiling.
What One Capsule Adds
A typical diet already supplies about 8 g of lysine a day, by a 1987 dietary study.[6]Assessment of dietary intake of lysine and arginine in patients with herpes simplex — Journal of the American Dietetic Association (1987) View source
- 1 capsule: 800 to 1,000 mg, depending on how the label counts.
- Added share: Roughly 10% to 12% of a typical day's lysine.
- 3 capsules: About 2,400 to 3,000 mg.
- Label directions: 1 capsule daily.
At the label dose, our 60-capsule lysine bottle sits far below every threshold above.
Antibiotics and Other Interactions
No human interaction study exists. One animal finding is worth knowing.
- Gentamicin: Lysine plus the antibiotic worsened kidney failure in rats.
- Other aminoglycosides: Tobramycin behaved the same way in that study.
- Arginine: Works against lysine's cold sore rationale.
- Calcium supplements: Absorption rises; mention it to your doctor.
The 1984 study found the combination produced substantially greater renal failure than either alone.[7]Nephrotoxicity of lysine and of a single dose of aminoglycoside in rats given lysine — Journal of Laboratory and Clinical Medicine (1984) View source
Pregnancy, Breastfeeding and Children
Food lysine is part of every diet. Supplement doses in these groups are simply unstudied.
- Pregnancy: 0 randomized trials of lysine supplements found.
- Breastfeeding: No published safety data at supplement doses.
- Children: 1 Ghana trial gave 1 g a day, in a lysine-poor setting.
- Our position: Ask your obstetrician or pediatrician first.
If a clinician agrees, start from the doses people actually take, not from the 6,000 mg ceiling.
Gallbladder and Heart: The Theoretical List
One review added cautions that rest on animal data rather than human cases.
- Gallbladder disease: Flagged as a theoretical risk.
- Heart disease: Flagged as a theoretical risk.
- Human cases: We found none for either.
- Practical step: Mention lysine if you have either condition.
The 2017 review advised cautioning patients with cardiovascular or gallbladder disease.[8]Lysine for Herpes Simplex Prophylaxis: A Review of the Evidence — Integrative Medicine (2017) View source
Stop and Speak to a Clinician 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
Is lysine hard on your kidneys? +
At trial doses, kidney problems were not a pattern. 1 case of kidney damage was published in 1996, and people with kidney disease were never studied, so ask first.
Is L-lysine hard on your liver? +
A PubMed search found 0 published human cases of liver injury from oral lysine. The 2019 review of 71 studies reported mainly stomach symptoms.
Who should not take lysine? +
People with kidney disease, anyone pregnant or breastfeeding without advice, and anyone on an aminoglycoside antibiotic. 1 review adds gallbladder and heart disease.
What supplements should not be taken with lysine? +
High-dose calcium is the one to discuss, since 800 mg of lysine raised calcium absorption in 1 study. Arginine works against lysine's cold sore rationale.
Is it safe to take 1000mg of lysine daily? +
For healthy adults the data say yes. 1,000 mg is a sixth of the 6,000 mg provisional level from a 2019 review of 71 studies.
Does lysine cause weight gain? +
We found 0 trials reporting weight gain from lysine. At 1 g a day it adds about 4 calories.
Can I take lysine while pregnant? +
We found 0 randomized trials of lysine supplements in pregnancy. Food lysine is normal; a supplement is a question for your obstetrician.
Does lysine cause kidney stones? +
We found 0 studies linking lysine supplements to kidney stones. It raised calcium absorption in 1 study, so mention it if you have had a stone.
Can lysine cause stomach problems? +
Yes, mildly. Nausea, stomach ache and diarrhea were the main effects across 71 studies; taking it with food is the usual first step.
Does lysine interact with antibiotics? +
In 1984 rat work, lysine plus gentamicin caused substantially worse kidney failure than either alone. 0 human studies exist, so tell your doctor.
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