Overview

Lysine is found in foods that contain protein and is also available over the counter as a dietary supplement. It is used for many reasons, but its benefits are not well defined. Lysine is usually well tolerated. Before taking lysine, tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is lysine used for?

Lysine is used for various reasons, but the benefits of lysine are not well defined. Some common reasons that people use lysine include the following.

• Cold sores
• To increase muscle strength
• To improve bone health

Note: The FDA has not reviewed lysine for safety and effectiveness. Learn more about dietary supplements here.

How does lysine work (mechanism of action)?

Lysine is an amino acid, which is a building block for protein. Your body uses lysine to make protein and produce energy.

Your body needs lysine to function, but it cannot make lysine on its own. As a result, you must get lysine from your diet. Lysine is naturally found in protein-rich foods, including meat, cheese, eggs, fish, beans, and tofu. Most people in the United States get enough lysine in their diet. Lysine can also be made in a lab and is found in dietary supplements. Product labels may list lysine as L-lysine, which is the same thing.

Lysine may help block the virus that causes cold sores (herpes simplex). But the benefits of taking lysine by mouth to prevent or treat cold sores are not well defined. Some studies have shown that lysine can help, but most studies have shown that it does not. Ointments that contain lysine are meant to be applied directly to a cold sore, but the benefits of these products are not well defined.

Since your body needs lysine to make protein, some people use lysine to help increase muscle strength. But it is not clear if lysine dietary supplements can help to build muscle. Lysine is sometimes also used to improve bone health, although it is not clear if or how lysine may work for this use.

How should I store lysine?

You should store lysine according to the product label. Most dietary supplements should be kept in a cool, dry location that is out of the reach of children and pets and not in direct sunlight.

Side Effects

What are the most common side effects of lysine?

Lysine is usually well tolerated. Tell your health care provider if you have any side effects that bother you.

There may be side effects of lysine that are not listed here. Contact your health care provider if you think you are having a side effect of a supplement. In the U.S., you can report side effects to the FDA at www.safetyreporting.hhs.gov or by calling 888-SAFEFOOD (888-723-3366). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of lysine?

While less common, the most serious side effects of lysine are described below, along with what to do if they happen.

Severe Allergic Reactions. Lysine may cause allergic reactions, which can be serious. Stop using lysine and get help right away if you have any of the following symptoms of a serious allergic reaction.

• Breathing problems or wheezing
• Racing heart
• Fever or general ill feeling
• Swollen lymph nodes
• Swelling of the face, lips, mouth, tongue, or throat
• Trouble swallowing or throat tightness
• Itching or skin rash
• Bumps on the skin called hives that can be red, pink, white, or brown depending on your skin tone
• Nausea or vomiting
• Dizziness, feeling lightheaded, or fainting
• Stomach cramps
• Joint pain

Precautions

Who should not use lysine?

Allergies to Ingredients. People who are allergic to any of the following should not use lysine.

• L-Lysine
• Lysine
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific lysine products they stock.

What should I know about lysine before using it?

Lysine is a dietary supplement. It cannot be marketed to treat or cure a disease.

Read and follow the directions on the specific product you are using, or use it as recommended by your health care provider.

Keep lysine out of the reach of children.

Lysine is available in many forms, including as a gummy, a dried ground powder, tablets, and capsules. It is also available as an ointment that can be applied to the skin. If you are taking lysine as a gummy, chew the gummy well before swallowing. If you are taking lysine powder, use an appropriate measuring device to measure the powder, such as the device included with the product. Read the label carefully and measure the amount stated on the label.

The FDA has not tested lysine products to confirm that they contain the ingredients stated on their labels. Some dietary supplements have been tested by third-party organizations to confirm that they contain the ingredients listed on their labels and do not contain any harmful chemicals. Learn more about how to choose a safe dietary supplement product here.

What should I tell my health care provider before using lysine?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if lysine is right for you.

In particular, make sure that you discuss any of the following.

Pregnancy. It is not known if or how lysine could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. Lysine passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does lysine interact with foods or drinks?

There are no known interactions between lysine and foods or drinks.

It is unknown if drinking alcohol will affect lysine.

Does lysine interact with medicines (drug interactions)?

There are no known interactions between lysine and medicines. Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

The interactions between lysine and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with lysine is incomplete. Always check with your health care provider before taking lysine with any medicines.

Dosing

What should I do if I accidentally use too much lysine?

If you or someone else has used too much lysine, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

Lysine is naturally found in foods that contain protein. It is also found in dietary supplements. Read the product label closely and speak with a health care provider about how to use lysine safely. Do not use double or extra doses, even if you miss a dose.