Go Ad-Free
logoThe People's Perspective on Medicine

How Good Is L-lysine Against Cold Sores?

There are few scientific trials testing the benefits of L-lysine against cold sores. But many readers say it works surprisingly well.

Cold sores are painful. They are also unsightly. Perhaps more alarming, there is some research to suggest that cold sores may increase the risk for Alzheimer’s disease (see this link). Consequently, we wonder if taking L-lysine could help protect the brain from dementia. See this link for a response to that question. A reader doubts there is science is behind using L-lysine against cold sores.

Is There Evidence on L-lysine Against Cold Sores?

Q. In my younger years, I suffered from recurring cold sores when exposed to the sun or when under stress. Back then I used a product called Enisyl (lysine spelled backwards). Fortunately, it worked immediately.

After this product disappeared, I found lysine supplements. Taking lysine at the first tingle could keep the cold sore from fully emerging or at least keep it as a small sore. I used a dosage of 500 mg three times a day, but I have no idea if that was correct.

A. Thank you for telling us about the product called Enisyl. There is currently a veterinary supplement for cats called Enisyl-F. It is available as chicken liver flavored chews and tuna flavored oral paste. This lysine product is marketed to support a healthy immune system. Some people use it to treat cats infected with feline herpes virus type 1 (FHV-1). This virus infects only cats and is not contagious to humans.

Human herpes simplex virus type 1 (HSV-1) causes cold sores. When levels of lysine are high within cells, the virus has difficulty replicating.

A review of the research in the journal Viruses (June 2023) reports that

“Lysine appears to be a successful daily prophylactic agent for reducing HSV recurrence, and is an effective therapeutic agent for decreasing the severity and healing time for HSV reactivation…lysine is a safe natural compound, without reported adverse side effects, and is a promising alternative treatment option for patients with HSV.”

Skeptic Rejects L-lysine as Useless Home Remedy:

Q. I’ve had cold sores since I was young. I have spoken with doctors about them innumerable times.

In your column, you often recommend taking L-lysine. This product has not shown efficacy in peer-reviewed clinical trials, as far as I’ve heard. It is just one of the home-remedy folk “cures” that show up in your columns. Even acyclovir and valacyclovir are of limited efficacy.

A. Cold sores are caused by herpes simplex virus type 1. It hides out in the body and appears in the form of a cold sore lesion on the lips or face in the event of a drop in immunity, exposure to intense sunlight or increased stress (BMJ Clinical Evidence, online Sep. 23, 2009).

A comprehensive Cochrane review did not include any studies on L-lysine against cold sores (Cochrane Database of Systematic Reviews, Aug. 7, 2015).  The analysis showed that long-term use of the antiviral drugs acyclovir or valacyclovir was modestly effective in preventing cold sores.

Stories About L-lysine Against Cold Sores:

Despite such negative news, we continue to hear from readers that L-lysine works for many people.

Here are just a few testimonials:

“Lysine tablets work for me. At the first tingle of a beginning cold sore, I take a 500 mg tablet. Then I take another 500 mg tablet later on that day.
“I try to take 1000 mg a day for several days. By then, there is either a small cold sore that goes away early or else no cold sore at all. Usually it’s the latter.”

Gael brings her biochemistry background to bear:

“I find L-lysine against cold sores to be very effective. I read recently that prevention is best, so I now take a 1,000 mg tablet each morning with breakfast.

“Having studied biochemistry long ago, I hypothesize that the herpes virus needs arginine to build its protein coat. Lysine is similar in structure to arginine; perhaps when there is more lysine than arginine, it inhibits the virus’s ability to replicate. If I do get the beginnings of a cold sore, I increase the dose to one tablet with each meal. I also try to avoid foods high in arginine, such as nuts and chocolate, when I have a cold sore.”

Nat has an interesting regimen to share:

“I used to get cold sores at least once every 2 months. And when I would have an outbreak, there would not be just one, but a whole CLUSTER of them in the same spot. So embarrassing and painful.

“I heard of L-Lysine and have been taking it. I don’t take it every day. As and when needed.

“If I look closely in the mirror and see a slight color change or texture change on my lips I take a 500mg tablet before bed or whenever I noticed it.

“When I feel like one is coming on I would up the dose to 1000 mg. DOES THE TRICK!

“I am not joking. Two days ago I woke up with the tell-tale bubble on the lip. I put ice in a sandwich bag and held the ice on my lip for 3 minutes (it kills the pain; feels like frostbite but helps to reduce the newly forming cold sore under the skin). Then I doused it with acyclovir antiviral cream. (I put a thin layer on if I am going to work; otherwise it’s embarrassing).

“Then as SOON as I saw it, I took 1000mg L-lysine. I find the cold sore diminished throughout the day. After work I slathered on cream and went to bed and the next morning. GONE!”

Share your own experience with L-lysine against cold sores in the comment section below.

Rate this article
4.5- 85 ratings
About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.”.
Tired of the ads on our website?

Now you can browse our website completely ad-free for just $5 / month. Stay up to date on breaking health news and support our work without the distraction of advertisements.

Browse our website ad-free
  • Chang JY et al, "Narrative review of alternative symptomatic treatments for herpes simplex virus." Viruses, June 2023. doi: 10.3390/v15061314
  • Worrall G, "Herpes labialis." BMJ Clinical Evidence, online Sep. 23, 2009.
Join over 150,000 Subscribers at The People's Pharmacy

We're empowering you to make wise decisions about your own health, by providing you with essential health information about both medical and alternative treatment options.