HealthWise® L-Lysine HCL is 100% pure pharmaceutical grade amino acid. Lysine is an essential amino acid and is a basic building block of all protein. This nutrient was first isolated in 1889 from casein. Vegan and strict vegetarian diets, using grains as the only source of protein can be deficient in this nutrient. Did you know? Lysine was the subject of the largest ever U.S. price-fixing court case, garnering a massive $100 million settlement and resulted in the conviction of 3 executives who served prison time for the offense. The case was the subject of "The Informant" - the 2009 film starring Matt Damon.