Lysine supplement: does it help cold sores?
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- L-lysine 500 mg capsules. Best for: Adults trying lysine for cold sore prevention. See options on Amazon
- L-lysine 1,000 mg tablets. Best for: People who want fewer pills at higher doses. See options on Amazon
- Lysine immune blend. Best for: Buyers comparing combination products. See options on Amazon
What lysine is
L-lysine is an essential amino acid, meaning the body cannot make it and must get it from food. A 2025 review in the Journal of Advanced Research notes it is a key building block of protein and has long been used to support children's growth in places where diets rely on cereals.
For adults, lysine is best known for cold sores. Lab studies suggest the herpes virus needs arginine-rich proteins to reproduce, and lysine competes with arginine, which is the theory behind its use.
What the research shows for cold sores
| Daily dose | What studies found |
|---|---|
| Under 1 g, no low-arginine diet | Appears ineffective |
| 624 mg or 750 mg | No significant prevention in controlled trials |
| 1 g to 1.26 g | Mixed: two trials helped, two did not |
| 3 g | Fewer recurrences and milder symptoms in one 6-month trial |
| Treating active sores | No convincing evidence |
The 2017 review in Integrative Medicine looked at 12 studies, 8 of them placebo controlled. In the 3 g trial, 74% of the lysine group reported milder symptoms versus 28% on placebo, though healing time did not differ. Only one older trial was included in a Cochrane review, which rated its evidence very low quality.
The authors concluded that longer controlled studies using more than 1.2 g a day are needed to test lysine properly.
Why the evidence is mixed
- Very common virus. The review estimates up to 90% of adults carry herpes simplex, which can reactivate with stress or immune problems, so outbreaks vary naturally.
- Diet confounds. Several trials combined lysine with a low-arginine diet, making it hard to separate the two.
- Dropouts and small samples. Many trials lost participants or were too small to be reliable.
- Surveys are weak evidence. In a survey of 1,543 people who bought lysine at health food stores, 88% said it worked, but self-selection and placebo effects were not accounted for.
- Doctors rarely advise it. A dose of 50 mg per kg of body weight was once suggested for cold sores, but conflicting evidence means doctors do not often recommend it.
Mouth ulcers
Herpes simplex has also been linked to recurring mouth ulcers (canker sores). In a small trial described in the review, 30 people with recurrent ulcers took 1,260 mg of lysine a day for 2 months, rising to 2,520 mg if early symptoms began. Ulcer recurrence decreased in 62.5% of the lysine group versus 14.2% on placebo, though ulcer duration and severity did not differ. The study was short and small.
Safety
- Generally safe. The review says doses up to 3 g a day are thought to be harmless, and oral lysine toxicity has not been reported in humans.
- Arginine balance. Because lysine may affect arginine, the review advises caution with cardiovascular disease, impotence, gallstones, asthma or immune problems.
- Digestive symptoms. The 2025 review notes side effects are mostly limited to stomach symptoms.
- Excess intake. Too much lysine can unbalance other amino acids.
- Pregnancy. NOW Foods advises a physician check if pregnant or nursing.
How to choose a lysine supplement
- Amount per capsule. NOW Foods' L-Lysine gives 500 mg (from 637 mg L-lysine hydrochloride) per capsule, 1 to 3 times daily.
- Match the evidence. Studies suggest doses under 1 g a day are unlikely to help cold sores; ask your doctor about higher amounts.
- Single ingredient. Immune blends add other ingredients; plain lysine matches the studies.
- Keep antiviral options in mind. Cold sores can be treated with prescription antivirals such as aciclovir, famciclovir or valaciclovir.
- See a doctor for frequent or severe outbreaks.
What to look for when you buy
L-lysine 500 mg capsules
Best for: Adults trying lysine for cold sore prevention
NOW Foods lists 500 mg L-lysine per capsule, taken 1 to 3 times daily.
Watch out: Studies suggest under 1 g a day is unlikely to help. Ask your doctor if you have heart or gallbladder disease.
See options on AmazonL-lysine 1,000 mg tablets
Best for: People who want fewer pills at higher doses
Lysine is also sold as 1,000 mg tablets.
Watch out: Keep total intake within label directions and talk with your doctor about doses above 1 g.
See options on AmazonLysine immune blend
Best for: Buyers comparing combination products
Some lysine products combine it with other ingredients.
Watch out: Blends were not what the cold sore studies tested. Check every ingredient.
See options on AmazonQuestions people ask
- Does lysine help cold sores?
- Possibly at higher doses for prevention. Under 1 g a day appears ineffective, and there is no convincing evidence it treats active sores.
- How much lysine should I take for cold sores?
- Studies suggesting benefit used about 1 g to 3 g a day. Talk with your doctor and follow the label.
- Is lysine safe?
- Doses up to 3 g a day are thought to be harmless. Use caution with heart disease, gallstones, asthma or immune problems.
- Does lysine help canker sores?
- One small 2-month trial found fewer recurrences, but more research is needed.
- What foods contain lysine?
- The 2025 review notes lysine supplements and lysine-fortified foods are used where diets rely mainly on cereals. Ask a dietitian about your own diet.
Sources
- Lysine for Herpes Simplex Prophylaxis: A Review of the Evidence (pmc.ncbi.nlm.nih.gov), Integrative Medicine (PMC6419779)
- L-lysine dietary supplementation for childhood and adolescent growth: Promises and precautions (pmc.ncbi.nlm.nih.gov), Journal of Advanced Research (PMC11976420)
- L-Lysine 500 mg Veg Capsules (www.nowfoods.com/products/supplements/l-lysine-500-mg-veg-capsules), NOW Foods