Lysine for Cold Sores: Does It Actually Work?

Cold sores can be a real pain in the mouth. And it’s hard to predict how big they’ll get or how long they’ll last. While there’s no cure for cold sores, treatments can help them go away faster — and prevent them from coming back. Lysine supplementation is one of these treatments that may help by interfering with the virus that causes cold sores.

What is lysine? 

Lysine is an essential amino acid, meaning the body doesn’t produce it naturally. Instead, you get lysine from the foods you eat. Amino acids make up proteins in your body. Lysine is important for many different bodily functions, like wound healing and the absorption of minerals like calcium. 

Scientists think that lysine helps with cold sores by blocking the production of another amino acid, arginine. The virus that causes cold sores — herpes simplex virus (HSV) — needs arginine to reproduce. Lysine may also prevent the absorption of arginine in your intestine, which could slow or prevent the replication and growth of HSV.

Lysine comes as a cream you can apply directly to a cold sore. It’s also available as an oral supplement, chewable, and powder forms. Most of the existing studies — and all those mentioned in this article — have looked at the oral supplement.

Do lysine supplements actually help with cold sores? 

Lysine may help prevent and treat cold sores, but research is limited. Some studies show that regularly taking lysine can help prevent outbreaks. Others show that it can both prevent cold sores and help them heal faster. 

One study shows that lysine lessens symptoms, shortens healing time, and prevents cold sores from returning. Another small study found that people who took 1,000 mg of oral lysine daily had smaller cold sores than usual during outbreaks. But it’s worth noting that these studies are older, and newer research is limited. 

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There’s no cure for HSV, so taking lysine doesn’t get rid of the virus completely. This means you could still get outbreaks, even if you take lysine.

How fast does lysine work on cold sores? 

More research is needed to know how fast lysine works on cold sores. But a couple studies have tried to answer this question.

One study compared adults who took lysine for a cold sore outbreak to those who didn’t. Cold sores completely resolved in 3 days for almost half of the people in the lysine group. And nearly all of them saw complete resolution by day 6. In comparison, healing time took up to 21 days for people who didn’t use lysine. 

A larger study surveyed over 1,500 people with cold sores. Of those who didn’t take lysine, 90% reported that healing took 6 to 15 days. In comparison, 83% of those who used lysine said their lesions healed within 5 days.

How much lysine should you take for cold sores? 

There’s no standardized dosage of lysine. Some studies have used 300 mg of lysine per day, while others have looked at the effects of 3,000 mg daily. 

In general, dosages range from 500 mg to 1,000 mg daily by mouth to prevent outbreaks. For active outbreaks, higher doses, like 3,000 mg (3 g), may be appropriate for a short period of time. 

Some experts suggest that lysine is safe at dosages up to 6,000 mg (6 g) daily. But most research recommends a maximum of 3 g per day. And you should only take it for a short period of time during active outbreaks. 

Instructions for over-the-counter (OTC) lysine cream suggest applying it as often as every 2 hours. But there’s no firm research to support that the cream definitely works.

While lysine is generally safe at the above doses, some people may experience unwanted side effects.

What are the risks of taking a lysine supplement? 

Common side effects of a lysine supplement may include:

• Nausea

• Abdominal pain

• Cramps

• Diarrhea

• Kidney problems

• Gallstones

Some people may want to avoid lysine completely because of side effects or safety concerns.

Who should not take lysine? 

You should not take lysine if you: 

• Are pregnant or breastfeeding: There isn’t enough research to know if lysine is safe during pregnancy or while breastfeeding. 

• Take calcium supplements: Lysine increases calcium absorption, which can lead to excessive calcium levels. Too much calcium can lead to muscle pain, weakness, bone pain, and other symptoms.

• Have gallstones: High doses of lysine can cause gallstones to form. If you have a history of gallstones, it’s best to avoid lysine.

You should also avoid lysine if you have a condition that lowers arginine levels, or are currently healing from a wound. This includes those with:

• Kidney disease

• Sickle cell disease 

• Recent surgery

• Recent trauma or injury

As with any supplement, consult with a healthcare professional before taking lysine. They can check to see if it’s safe for you, or if there are any potential interactions with your other medications.

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Written by:

Cherilyn Davis, MD

Cherilyn Davis, MD, is a board-certified pediatrician in New York City. She has held local and national roles at the American Medical Women’s Association including board member of the physician division and physician chair of social media.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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