Overview

L-arginine is an amino acid that is naturally found in foods. It is also available over the counter as a supplement. L-arginine is sometimes used to reduce blood pressure, relieve chest pain, and help with erectile dysfunction. Although L-arginine may provide some benefit for these uses, it may not offer enough benefit to help manage these conditions. L-arginine may also be used to improve athletic performance, but its benefits are not well defined. Common side effects include diarrhea and an upset stomach, especially with high doses. Before taking L-arginine, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is L-arginine used for?

L-arginine is used for many reasons, although its benefits for most uses are not well defined. Some common reasons for using L-arginine include the following.

• Chest pain (angina)
• Erectile dysfunction
• High blood pressure
• Migraine
• To improve athletic performance

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

L-arginine is available as a dietary supplement in various strengths and dosage forms. Since it is an amino acid, it is also found in many protein powders. It may also be included in products that contain other ingredients, such as caffeine and vitamins.

How does L-arginine work (mechanism of action)?

L-arginine is an amino acid, which is a building block of protein. Your body makes L-arginine on its own, but it is also found in many foods, including meat, fish, dairy, nuts, seeds, soy, and legumes. Your body uses L-arginine for many reasons, such as for muscle function, to build protein, and to produce nitric oxide (NO).

Nitric oxide is a gas that is naturally made by your body to help relax your blood vessels, which helps lower blood pressure and increase blood flow throughout your body. L-arginine plays an important role in how your body makes nitric oxide. This has led to interest in using L-arginine to lower high blood pressure, reduce chest pain (angina) related to heart problems, and help with erectile dysfunction. Most research shows that taking L-arginine may provide small improvements in people with these conditions. But it is important to talk to your health care provider before taking L-arginine. L-arginine may not provide enough benefit to help manage your condition. And if you are already taking prescription medicines for any of these reasons, L-arginine may increase your risk of side effects.

Since L-arginine can help relax blood vessels and improve blood flow, there is also interest in using it to improve muscle function during exercise. But the benefits of L-arginine for athletic performance are not well defined. In some people who do certain types of exercise, it may help improve performance by a small amount. However, some studies show that it does not help with performance at all.

How should I store L-arginine?

You should store L-arginine 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 L-arginine?

The most common side effects of L-arginine are diarrhea and an upset stomach. These side effects may vary depending on which product you are using and may be more likely if you are taking high doses. Tell your health care provider if you have any of these side effects that bother you.

There may be other side effects of L-arginine 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 L-arginine?

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

Severe Allergic Reactions. L-arginine may cause allergic reactions, which can be serious. Stop taking L-arginine 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 L-arginine?

Allergies to Ingredients. People who are allergic to any of the following should not take L-arginine.

• Arginine
• L-arginine
• Any of the ingredients in the specific product

Your pharmacist can tell you all of the ingredients in the specific L-arginine products they stock.

What should I know about L-arginine before using it?

L-arginine 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 L-arginine out of the reach of children.

L-arginine may be found in some supplements that are marketed as “nitric oxide (NO) boosters.” Since nitric oxide is a gas, it cannot be taken as a supplement. Instead, products that claim to boost nitric oxide levels contain substances that may help increase nitric oxide levels in the body. L-arginine is one of these substances. But these products may also contain many other ingredients that can have various effects on the body. Read the product label carefully to see which ingredients it contains.

Some dietary supplements that contain L-arginine also contain caffeine. However, dietary supplements and non-soda beverages are not required to state their caffeine content. Use these products with caution, especially if you are sensitive to caffeine or you regularly drink caffeinated beverages. Too much caffeine can increase your risk for side effects.

Do not confuse nitric oxide, a gas that is naturally found in your body, with nitrous oxide (laughing gas), which is sometimes used during dental procedures. These gases are not the same and have very different effects and side effects.

The FDA has not tested L-arginine 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 L-arginine?

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 L-arginine is right for you.

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

Current and Past Health Conditions.Tell your health care provider if you have any of the following.

• Blood vessel problems, including peripheral vascular disease
• Heart problems, including a past heart attack
• High blood pressure
• Kidney or liver problems

Other Medicines and Supplements.L-arginine may interact with other medicines and supplements. Before taking L-arginine, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

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

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

Interactions

Does L-arginine interact with foods or drinks?

There are no known interactions between L-arginine and foods or drinks.

It is unknown if drinking alcohol will affect L-arginine.

Does L-arginine interact with medicines (drug interactions)?

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.

In particular, make sure that you discuss if you are using any of the following before taking L-arginine.

• A medicine for high blood pressure
• A nitrate, such as nitroglycerin (Nitro-Dur, NitroMist, Nitrostat, and others), isosorbide dinitrate (Isordil), or isosorbide mononitrate, which is a medicine used to prevent or treat short-lasting chest pain caused by a type of heart disease
• A phosphodiesterase 5 (PDE5) inhibitor, such as avanafil (Stendra), sildenafil (Viagra, Revatio, and others), tadalafil (Cialis and others), or vardenafil (Levitra, Staxyn), which is a medicine used for erectile dysfunction or pulmonary arterial hypertension (PAH)

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

Dosing

What should I do if I accidentally use too much L-arginine?

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

L-arginine comes in a wide range of doses depending on your reasons for using it. It may also be combined with other ingredients. Read the product label closely, and speak with a health care provider about how to take L-arginine safely. Do not take double or extra doses, even if you miss a dose.