Lysine

amino acid

Best with a mealTake with food

What is it

Lysine is an essential amino acid that the body cannot synthesize and must obtain from food. It is needed for protein synthesis, calcium absorption, collagen formation, carnitine production, and immune function. Supplements use the L-lysine form.

How it works

Lysine plays structural and metabolic roles throughout the body. It is essential for protein synthesis, with particular importance for the cross-linking of collagen and elastin that gives connective tissue its strength. Lysine is a precursor for carnitine, which shuttles fatty acids into mitochondria for energy production. It helps the body absorb and conserve calcium, and supports immune function. The most distinctive supplemental use of L-lysine is for herpes simplex management. Herpes simplex virus (HSV-1 for oral cold sores, HSV-2 for genital herpes) requires arginine for replication; lysine and arginine share intestinal absorption and metabolic pathways, so high lysine intake may indirectly limit arginine availability to the virus. Trials have shown reduced outbreak frequency and severity in people taking 1 to 3 grams of lysine daily, with effect sizes that are modest but consistent. Lysine is also being investigated for migraine prevention and bone health, though evidence is less mature.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Herpes simplex prevention and treatment

Grade C

Moderate evidence

Multiple older trials at 1 to 3 g/day have shown reduced frequency and severity of cold sores and genital herpes outbreaks. A 1987 randomized trial in 52 patients showed 3 g/day for 6 months reduced outbreak frequency from 5.0 to 3.1 episodes per 6-month period. Effects are modest, and severe outbreaks still warrant antiviral medication.

Calcium absorption and bone health

Grade C

Moderate evidence

Lysine supplementation has shown modest increases in calcium absorption and reduced urinary calcium excretion in small studies. Effects on actual bone mineral density or fracture risk have not been adequately demonstrated.

Anxiety reduction

Grade C

Moderate evidence

Combination supplements of lysine plus arginine have shown reductions in chronic and acute anxiety in some trials, possibly via modulation of stress-related neurotransmitter systems. Evidence is limited.

Migraine prevention

Grade D

Mixed evidence

Limited preliminary data suggest lysine may reduce migraine frequency. Mechanism is unclear and evidence base is small. Not a standard recommendation.

Wound healing

Grade D

Mixed evidence

Lysine's role in collagen synthesis provides a plausible mechanism for wound healing support. Controlled trials specifically testing lysine alone for wound outcomes are limited.

3 commercial forms

L-lysine HCl

Hydrochloride salt; well absorbed orally.

The most common consumer form, available as capsules, tablets, or powder. Affordable and well-studied for herpes prevention.

L-lysine monohydrate

Equally well absorbed as HCl form.

Alternative salt form with similar effects.

Lysine + vitamin C combinations

Vitamin C supports collagen synthesis where lysine is a key residue.

Marketed for skin, joint, and collagen support. The combination is biochemically rational but not proven to outperform either alone.

Dosage

The RDA for adults is 38 mg per kilogram body weight per day, easily met by typical diets containing animal protein. Plant-based diets centered on grains may run lower because cereals are low in lysine. Supplemental doses for herpes prevention are 1 to 3 grams per day, with higher doses (3 to 6 g) used during active outbreaks for 7 to 14 days. Doses for other uses are typically 1 to 2 grams per day.

When and how to take it

For ongoing herpes suppression, take 1 gram of L-lysine once daily, with or without food. During an active outbreak, increase to 3 grams per day in divided doses (1 gram three times daily) for 7 to 14 days, ideally on an empty stomach to avoid competition with arginine in protein-rich meals. Lysine and arginine compete for the same intestinal transporter; if you take both, separate them by several hours. Taking lysine with vitamin C may modestly support collagen synthesis. Cool, dry storage preserves potency.

Food sources

Food	Amount	%DV
Beef (3 oz)	~2.4 g	—
Chicken breast (3 oz)	~2.5 g	—
Salmon (3 oz)	~2 g	—
Cottage cheese (1 cup)	~2.2 g	—
Eggs (1 large)	~0.5 g	—
Tempeh (1/2 cup)	~0.9 g	—
Lentils (1 cup cooked)	~1.2 g	—
Greek yogurt (1 cup)	~1.7 g	—

Safety

L-lysine is well tolerated at typical doses. Side effects are uncommon and mild: abdominal cramping, diarrhea, or kidney stones at very high chronic doses. Chronic intakes above 6 grams per day are not well studied. No formal Tolerable Upper Intake Level has been established. The most notable safety consideration is in kidney disease: lysine can accumulate when renal function is impaired and may worsen tubular damage in some animal models. People with chronic kidney disease should consult a clinician before supplementing. High-dose lysine combined with high calcium intake can theoretically increase calcium absorption beyond desired levels.

Who should be cautious

Use cautiously with chronic kidney disease, liver dysfunction, hypercalcemia, or osteoporosis (potential calcium absorption effects). Pregnant and breastfeeding women should rely on dietary intake. People with lysinuric protein intolerance, a rare genetic disorder, should avoid supplementation. Coordinate with prescribers if taking calcium supplements at high doses.

Interactions

L-lysine may increase calcium absorption, which could compound effects of calcium supplements. It can compete with arginine for intestinal absorption, potentially reducing the effectiveness of arginine supplements. Calcium-fortified products may affect lysine absorption. Combined with high-dose calcium, hypercalcemia is a theoretical risk. No major interactions reported with most prescription medications.

Frequently asked questions

Does lysine actually prevent cold sores?⌄

Probably modestly. Multiple older trials showed reduced outbreak frequency at 1 to 3 g/day. Effects aren't dramatic and won't replace antiviral medication for severe outbreaks, but as a low-cost daily supplement it has a plausible mechanism and reasonable evidence.

Can I take lysine and arginine together?⌄

Yes, but separate them by several hours because they compete for the same intestinal transporter. If your goal is arginine effects (NO production), don't take lysine close to it.

How much lysine is in a typical diet?⌄

Adults eating roughly 70 grams of protein per day, including animal sources, easily exceed the 38 mg/kg/day RDA. Plant-based diets centered on grains (which are low in lysine) and legumes (which are higher) are mostly adequate if the foods are varied.

Is lysine safe long-term?⌄

At doses up to 3 g/day for months, lysine appears well tolerated. Chronic doses above 6 g/day have not been well studied, and very high doses may stress the kidneys. People with kidney disease should consult a clinician.

What's the difference between L-lysine and lysine HCl?⌄

L-lysine is the biologically active form; HCl is just the salt that stabilizes it. L-lysine monohydrate is another form. All are absorbed similarly. The 'L' refers to the chiral form found in nature.

References

Wikidata: Lysine — Wikidata link

Track Lysine with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.