uses JavaScript to provide the best possible experience for our content, but your browser has it disabled. Learn how to enable it here.


Watch the video


What to look for on L-lysine labels?

  • What is lysine?

    Lysine (L-lysine) is an essential amino acid found in many protein-rich foods (see Lysine in Food) and is needed for proper growth and other critical functions (see details in What It Is).
  • What are the health benefits of lysine?

    As a supplement, some (but not all) studies suggest that lysine may help prevent cold sores (herpes simplex labialis), genital herpes lesions, and canker sores. There is no clinical evidence, however, that lysine helps treat an existing herpes eruption. It has been used in studies of hair loss treatment, but results are not convincing. There is no clinical evidence that lysine helps prevent or treat COVID-19, nor herpes 1 infection in cats. Although lysine is also found in topical products for cold sores, it is not known to be active topically (see details in What It Does).
  • How much lysine to take?

    Typical daily dosage is 1,000 to 3,000 mg (1 to 3 grams) (see details in ConsumerTips).
  • The best lysine supplement:

    CL's tests found that all of the selected L-lysine products contained their listed amounts of lysine, with some providing a bit more (see details in What CL Found). However, some products were a much better value than others, with the cost ranging from as little as 5 cents to as much as 32 cents to obtain 1,000 mg of L-lysine (and up to 49 cents from a cat product). Based on quality and value, ConsumerLab selected Top Picks among lysine supplements including a lysine supplement for cats.
  • L-lysine is typically sold as its stabilized salt form, called L-lysine HCl (L-lysine hydrochloride). Be aware that 20% of the weight of L-lysine HCl is HCl and not L-lysine. Well-labeled lysine supplements will list the amount of L-lysine (since this is the active ingredient) and deduct the weight of the HCl. However, some products (including two in this Review) list the weight of the full compound (i.e., lysine plus HCL), which can lead unwitting consumers to believe they are getting more lysine than they think (see examples in What CL Found).
  • Lysine safety and side effects:

    People with kidney disease, gallstones, elevated cholesterol, and glutaric acidemia type I should exercise caution with lysine supplements (see details in Concerns and Cautions).

Make sure you're choosing the best lysine supplements approved in our tests!

See the Full Review as a Member

Join now at

Lysine supplement brands compared in this review

View Larger Image 8342_large_Carlson-L-Lysine-Powder-Lysine-2023.PNG

Carlson L-Lysine Powder

View Larger Image 8349_large_Coco_and_Luna-L-Lysine-Powder-Lysine-2023.PNG

Coco and Luna L-Lysine - Salmon Flavor - Cat

View Larger Image 8344_large_CVS_Health-L-Lysine-1000mg-Lysine-2023.PNG

CVS Health L-Lysine 1,000 mg

View Larger Image 8343_large_GNC-L-Lysine-1000mg-Lysine-2023.PNG

GNC L-Lysine

View Larger Image 8345_large_LifeExtension-L-Lysine-620mg-Lysine-2023.PNG

Life Extension L-Lysine 620 mg

View Larger Image 8347_large_NOW-Double_Strength_L-Lysine_1000mg-Lysine-2023.PNG

NOW Double Strength L-Lysine 1,000 mg

View Larger Image 8346_large_Pure_Encapsulations-I-Lysine-Lysine-2023.PNG

Pure Encapsulations L-Lysine

View Larger Image 8350_large_Simple_Truth-L-Lysine-500mg-Lysine-2023.PNG

Simple Truth Free Form L-Lysine 500 mg

View Larger Image 8341_large_Spring_Valley-L-Lysine-1000mg-Lysine-2023.PNG

Spring Valley L-Lysine 1,000 mg

View Larger Image 8348_large_Swanson-L-Lysine-500mg-Lysine-2023.PNG

Swanson L-Lysine

You must be a member to get the full test results along with's Top Picks among products. You'll get results for 10 popular lysine supplents (including one for cats), including 9 products selected for testing by, and one additional product that passed the same testing through CL's voluntary Quality Certification Program.

You'll get all of the following information about lysine supplements in this comprehensive review:

  • Which lysine supplements passed or failed ConsumerLab's tests.
  • CL's Top Picks among lysine supplements based on quality and value.
  • What lysine can and cannot do for your health, and your cat's health.
  • How to read the labels, so you know how much lysine you can really expect from a product without being fooled.  
  • Lysine dosage for uses including cold sores, genital herpes lesions and canker sores.
  • Concerns, drug interactions, and potential side-effects of lysine.

Join to unlock the full report and get full access to over 1,400 reviews

See the Full Review as a Member

Join now at

Additional Information
Tested through CL's Quality Certification Program prior to, or after initial posting of this Product Review.