Product Reviews
Lysine Supplements Review

Reviewed and edited by Tod Cooperman, M.D. Tod Cooperman, M.D.
Posted: 2/6/2016  Last update: 4/7/2020

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  • 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).
  • 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).
    • COVID-19 UPDATE: Due to its potential antiviral and immune-stimulating properties, lysine is being promoted fight coronavirus (SARS-CoV-2) infection (COVID-19). However, there is no evidence at this time to suggest taking lysine supplements can help prevent or treat COVID-19. See the COVID-19 section section for details.
  • 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).
  • CL's tests found that all but one product contained their listed amounts of lysine (see details in What CL Found).
  • Best value: 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.
  • People with kidney disease, gallstones, elevated cholesterol, and glutaric acidemia type I should exercise caution with lysine supplements (see details in Concerns and Cautions).
What It Is:
Lysine is an essential amino acid, meaning that it must be obtained from foods, because the body is unable to make it. It is important for proper growth, and is involved in the production of collagen as well as calcium absorption. Most people need about 1 gram per day, which can typically be provided by a 100 gram (3.5 oz) serving of protein rich food such as beef or poultry, eggs or cheese. Vegetarian sources include tofu, beans, nuts such as peanuts and almonds, and sunflower seeds. (See Lysine in Foods table below for amounts found in individual foods.) 

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