Overview

L-citrulline is an amino acid that is naturally found in watermelons and other foods. It is also available over the counter as a supplement. L-citrulline is sometimes used to lower blood pressure and improve athletic performance, but its benefits for most uses are not well defined. A common side effect is an upset stomach. Before taking L-citrulline, make sure to tell your health care provider about any health conditions you have or medicines you are taking.

Uses

What is L-citrulline used for?

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

• High blood pressure
• Preeclampsia
• To improve athletic performance
• To reduce muscle damage after exercise

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

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

L-citrulline is an amino acid, which is a building block of protein. Your body makes L-citrulline on its own, but it is also found in some foods, including watermelons, other melons, squash, cucumbers, pumpkins, and chickpeas. Your body uses L-citrulline to make another amino acid called L-arginine. Taking L-citrulline can increase the levels of L-citrulline and L-arginine in your body. L-arginine has many functions, including building protein, improving muscle function, and producing 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. Your body turns L-citrulline into L-arginine, which plays an important role in making nitric oxide. This has led to interest in using L-citrulline to lower high blood pressure in adults who have hypertension and in people with a condition that occurs during pregnancy called preeclampsia. But the benefits of L-citrulline for any use are not well defined. Some studies show that it may be able to reduce blood pressure by a small amount, but this amount may not be clinically meaningful.

There is also interest in taking L-citrulline or watermelon juice to improve muscle function during exercise or to reduce muscle damage from exercise. But the benefits of L-citrulline for these uses are unclear. While it may have small effects in some people, it may not have any benefits in other people.

How should I store L-citrulline?

You should store L-citrulline 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-citrulline?

The most common side effect of L-citrulline is an upset stomach. Side effects may vary depending on the dose you are taking or the specific product you are using. Tell your health care provider if you have any side effects that bother you.

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

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

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

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

• Citrulline
• Citrulline malate (Citmal)
• L-citrulline
• Any of the ingredients in the specific product

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

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

L-citrulline 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 taking, or take it as recommended by your health care provider.

Keep L-citrulline out of the reach of children.

L-citrulline 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, these products contain substances that may help increase nitric oxide levels in the body. L-citrulline 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-citrulline 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-citrulline 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-citrulline?

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-citrulline 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-citrulline may interact with other medicines and supplements. Before taking L-citrulline, 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-citrulline could affect pregnancy or harm a fetus. Tell your health care provider if you are pregnant or plan to become pregnant.

Breastfeeding. It is not known if L-citrulline passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed.

Interactions

Does L-citrulline interact with foods or drinks?

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

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

Does L-citrulline 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-citrulline.

• 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 (PDE-5) inhibitor, such as avanafil (Stendra), sildenafil (Revatio, Viagra, 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-citrulline and medicines are not fully understood. As with most dietary supplements, the research on drug interactions with L-citrulline is incomplete. Always check with your health care provider before taking L-citrulline with any medicines.

Dosing

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

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

L-citrulline is found in watermelons, watermelon juice, and dietary supplements. Products that contain L-citrulline often contain other ingredients as well. Read the product label closely, and speak with a health care provider about how to take L-citrulline safely. Do not take double or extra doses, even if you miss a dose.