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  • 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, lysine may help prevent cold sores (herpes simplex labialis), genital herpes lesions, and canker sores. Although it 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 (see details in Quality Concerns).
  • Lysine has also been used to prevent/treat feline herpesvirus 1 infection — but there is no clinical evidence to support this use and it is not recommended (see details in What It Does, For Cats).
  • What did CL's tests of lysine find? CL's tests found that all but one product contained their listed amounts of lysine (see details in What CL Found).
  • Best value for lysine: The cost to obtain lysine from CL Approved products ranged from 4 cents to 33 cents per 1,000 mg (and up to 72 cents for cat products). See which CL Approved products provide the best value.
  • To compare product test ratings, ingredients, and prices, see the Results Table.
  • 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).

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Lysine supplement brands compared in this review

View Larger Image 5081_small_21stCentury-Lysine-Small-2016.jpg

21st Century L-Lysine for Cats

View Larger Image 5064_small_AndrewLessman-Lysine-Small-2016.jpg

Andrew Lessman ProCaps Lysine

View Larger Image 5065_small_Carlson-Lysine-Small-2016.jpg

Carlson L-Lysine

View Larger Image 5066_small_CVSPharmacy-Lysine-Small-2016.jpg

CVS/pharmacy L-Lysine

View Larger Image 5067_small_DouglasLabratories-Lysine-Small-2016.jpg

Douglas Laboratories L-Lysine

View Larger Image 5068_small_FinestNutrition-Lysine-Small-2016.jpg

Finest Nutrition [Walgreens] L-Lysine

View Larger Image 5069_small_GNC-Lysine-Small-2016.jpg

GNC L-Lysine

View Larger Image 5070_small_NatureMade-Lysine-Small-2016.jpg

Nature Made L-Lysine

View Larger Image 5082_small_PetNaturalsOfVermont-Lysine-Small-2016.jpg

Pet Naturals of Vermont L-Lysine for Cats

View Larger Image 5071_small_PuritansPride-Lysine-Small-2016.jpg

Puritan's Pride L-Lysine

View Larger Image 5072_small_Rexall-Lysine-Small-2016.jpg

Rexall L-Lysine

View Larger Image 5083_small_RiteAid-Lysine-Small-2016.jpg

Rite Aid Pharmacy L-Lysine

View Larger Image 5073_small_Solaray-Lysine-Small-2016.jpg

Solaray L-Lysine

View Larger Image 5074_small_Solgar-Lysine-Small-2016.jpg

Solgar L-Lysine

View Larger Image 5075_small_SourceNaturals-Lysine-Small-2015.jpg

Source Naturals L-Lysine

View Larger Image 5076_small_SpringValley-Lysine-Small-2016.jpg

Spring Valley [Walmart] L-Lysine

View Larger Image 5077_small_Swanson-Lysine-Small-2016.jpg

Swanson Free-Form L-Lysine

View Larger Image 5078_small_UpAndUp-Lysine-Small-2016.jpg

Up & Up [Target] L-Lysine

View Larger Image 5079_small_Vitacost-Lysine-Small-2016.jpg

Vitacost L-Lysine

Vitamin World L-Lysine

In this comprehensive review of lysine supplements, you'll get test results and quality ratings for 17 lysine supplements for people (including 7 that passed our voluntary Quality Certification Program) and two popular lysine supplements for cats. You'll also get information about an additional lysine supplement similar to one that passed testing. You'll learn:
  • Which lysine supplements passed or failed testing 
  • How lysine supplements compare on quality and cost and which provide the best 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.

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