L-lysine for cold sores: dose, the evidence, and cost

Short version: people take 1-3 g of L-lysine a day for cold sores, the evidence that it helps is mixed rather than settled, and it is one of the cheapest supplements you can buy per dose — which is exactly why it is a low-stakes thing to try. This page is a value guide, not medical advice.

What L-lysine is

Lysine is an essential amino acid, meaning your body cannot make it and you have to get it from food. It is abundant in meat, fish, eggs, and dairy, and it is a building block your body uses for protein and connective tissue. As a supplement it is sold as plain L-lysine in capsules, tablets, and powder. Because it is a commodity amino acid, the active ingredient is the same across brands.

The cold-sore dose

Cold sores are caused by the herpes simplex virus (usually HSV-1), which stays dormant in the body and flares up periodically. The lysine amounts people use fall into a familiar range:

• Around 1-3 g per day total.
• Some people take the higher end during an active outbreak and a lower amount

as ongoing maintenance between flare-ups.

These are the figures commonly cited in the supplement world. They are a starting point for comparison, not a personalized medical dose.

The honest state of the evidence

This is the part most product pages skip, so here it is plainly: **the research is mixed.**

• Some studies have reported that lysine may reduce how often cold sores come

back, or make outbreaks less severe or shorter.

• Other studies found no clear benefit.
• The trials are generally small, use different doses, and do not add up to a

firm conclusion.

So lysine is best described as a **cheap, low-risk option some people find helpful**, not a treatment with strong proof behind it. If cold sores are frequent or severe, prescription antiviral medication has far better evidence, and that is a conversation for a clinician.

The lysine-versus-arginine theory

The reasoning behind lysine is worth understanding, because it explains why the supplement even exists:

• The herpes virus appears to rely on the amino acid arginine to replicate.
• Lysine is structurally similar to arginine and may compete with it.
• The idea is that tilting the balance toward lysine and away from arginine makes

conditions less friendly for the virus.

This is a plausible biological mechanism. It is important to keep the distinction clear, though: a sensible-sounding mechanism is not the same as a proven result in people, which is why the actual outcome data still matters more than the theory.

Safety

Lysine is an amino acid you already eat every day in any protein-containing meal, and at the 1-3 g amounts people use it is generally well tolerated. The most common complaint is mild stomach upset. As with any supplement taken in gram amounts, people who are pregnant, have kidney issues, or take prescription medication should check with a clinician first. This page is not medical advice.

Why cost per dose is easy here

Lysine is one of the least expensive supplements on the shelf. The active ingredient is identical across brands, so the smart way to buy is by **cost per gram of lysine**, not cost per bottle. A few pointers:

• Read the label amount. A "1000 mg" tablet is 1 g, so a 3 g day is three of

them. Do the arithmetic before comparing prices.

• Powder is cheapest per gram if you do not mind measuring; capsules and

tablets cost more for the convenience.

• Ignore "high potency" branding — the molecule is the same. You are only ever

paying for milligrams of lysine plus format.

The honest bottom line

• The commonly used cold-sore dose is 1-3 g of L-lysine per day.
• The evidence is mixed, so treat lysine as a cheap experiment, not a cure, and

see a clinician for frequent or severe outbreaks.

• It is safe for most people at these amounts and very cheap, so buy on **cost per

gram**.

Check live listings on the L-lysine nutrient page, compare the best-value L-lysine options ranked by cost per dose, and see how we calculate that in our methodology. Not medical advice.