Research indicates that the global market for dietary supplements was already booming in 2021, valued at over $152 billion. Expectations suggest this market could skyrocket to around $300 billion by 2028.

In the U.S., dietary supplements aren’t regulated by the Food and Drug Administration (FDA) in the same way as food and pharmaceuticals. Many widely-used supplements have been found to be ineffective or even harmful in large doses. However, the majority of supplements available are generally deemed safe when consumed as directed.

L-Lysine is one of the most popular supplements, but registered dietitians typically don’t recommend it unless you have a medical condition or dietary limitation that prevents you from obtaining sufficient amounts from natural food sources.

What is L-Lysine?

L-Lysine, commonly referred to simply as lysine, is an amino acid—a type of organic molecule that combines to form proteins. It is classified as an essential amino acid because our body cannot produce it independently. As Dr. Walter Willett, a physician and professor at Harvard T.H. Chan School of Public Health, explains, “Lysine is crucial for building proteins in every cell of our body.”

Since our body doesn’t synthesize lysine, we must acquire it through our diet. Luckily, “most healthy Americans are adequately supplied with protein,” Willett notes. Lysine is prevalent in many protein-rich foods such as eggs, various meats (like pork, beef, chicken, and fish), and dairy products (including milk, yogurt, and cheese). Additionally, it can be found in whole plant foods like wheat and beans.

In essence, if you maintain a balanced diet, you’re likely already consuming enough lysine and other necessary amino acids.

However, individuals with specific medical conditions or dietary restrictions that lead to protein deficiency may be advised to supplement with L-Lysine.

L-Lysine can be found in various forms: pills, powders, liquids, and creams.

What Are the Benefits of L-Lysine?

Lysine offers several important health benefits. It helps the body absorb calcium, which is vital for bone health; it supports immune function by aiding in antibody production; and research indicates that it may alleviate stress and anxiety by lowering cortisol levels. Additionally, it plays a key role in protein synthesis, including the production of enzymes and hormones, as well as tissue growth and repair. Lysine is also significant for collagen formation, making it essential for skin health.

Nevertheless, most people gain these benefits by consuming a diverse range of healthy foods.

L-Lysine supplements are especially recommended to help prevent herpes outbreaks, particularly cold sores, according to Dr. Denise Millstine, a women’s health specialist at the Mayo Clinic. However, she cautions that while lysine is effective at preventing outbreaks, there is limited research supporting its efficacy in treating an active cold sore. The antiviral properties of lysine help inhibit arginine, which encourages the replication of the herpes virus, as noted by Mount Sinai Hospital in New York.

The function of lysine in enhancing muscle and bone structure is part of why it’s often marketed to bodybuilders, Willett explains, although there’s no scientific support for using it as a bodybuilding supplement.

Lysine is also said to promote a robust immune system, and while some animal studies suggest a possible mechanism, this effect hasn’t been demonstrated in human research yet, Millstine clarifies.

Is It Safe to Take L-Lysine Supplements?

Despite the lack of strong scientific backing for using lysine as a supplement for enhancing athletic performance, improving skin quality, or preventing illness, consuming up to 3,000 milligrams (3 grams) daily is generally considered safe for most individuals.

Taking lysine in excessive amounts can lead to digestive issues such as upset stomach and diarrhea, Millstine cautions. Additionally, Willett notes there may be unknown risks associated with long-term use, as these effects have not been widely researched.

“Aside from using it to prevent herpes outbreaks,” Millstine concludes, “it’s typically adequate to derive L-Lysine from protein-rich foods.”

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