L-citrulline is an amino acid naturally made in your body. While most amino acids build proteins, L-citrulline helps to form arginine (which helps build proteins), nitric oxide, and urea.

Arginine and L-citrulline also help produce nitric oxide, which plays a role in dilating (relaxing) your blood vessels.

L-citrulline is naturally found in watermelon and can be taken as a supplement. It may help improve exercise performance, lower blood pressure, and manage blood sugar.

L-citrulline may be useful in treating and managing certain conditions, including improved exercise performance, blood pressure, and blood sugar.

Improve Exercise Performance

Taking L-citrulline before exercise may lower exhaustion and improve muscle soreness. This is likely due to L-citrulline’s role in nitric oxide production. Nitric oxide opens the blood vessels, which improves blood flow, sending more oxygen and nutrients to your muscles. This can help with recovery, soreness, and strength.

Most available studies used a one-time dose of 3-9 grams of L-citrulline before exercise. A few researchers have evaluated seven days’ worth of L-citrulline. The type of exercise performed also varied among studies. Overall, data is conflicting on how useful the amino acid is in exercise performance. More well-controlled studies are needed to understand the potential benefits of L-citrulline in exercise.

Improve Blood Pressure

L-citrulline may be useful in lowering blood pressure. In the body, L-citrulline is converted to arginine, which increases nitric oxide levels. Nitric oxide opens your blood vessels, reducing blood pressure.

The data on L-citrulline in blood pressure control is conflicting. Many studies have found that the amino acid does lower blood pressure, though not significantly. Other studies have found that L-citrulline has minimal or no effect on blood pressure. More well-controlled studies are needed to evaluate L-citrulline’s role in blood pressure management.

Improve Blood Sugar

L-citrulline may help lower blood sugar and manage diabetes. L-citrulline’s role in increasing nitric oxide can help improve blood vessel dilation and insulin sensitivity (how well insulin works in your body).

High blood sugar and diabetes can also cause changes in your vascular (blood vessel) system that can lead to the development of complications such as diabetic neuropathy (nerve damage), heart disease, and stroke. L-citrulline’s nitric oxide effect may help reduce these complications.

Small studies have found that L-citrulline may improve blood sugar and act as an antioxidant, further improving type 2 diabetes and high blood sugar complications. One study found that L-citrulline improved blood sugar, cholesterol levels, and inflammation in people with type 2 diabetes. However, another study found that L-citrulline did not improve insulin sensitivity and inflammation in people with type 2 diabetes after eight weeks.

More research is needed to understand the role L-citrulline may play in treating diabetes and lowering blood sugar.

There is no recommended daily intake level or dose of L-citrulline. In adults, L-citrulline dosing typically ranges from 1.5-5 grams daily for four months or 6-12 grams in a single dose. Safe L-citrulline dosing is not currently available for children.

L-citrulline has not been studied in people who are pregnant or breastfeeding. Therefore, it is not recommended you take the supplement during these times.

Talk with your healthcare provider if you are interested in taking L-citrulline. They can help you determine if the supplement would be beneficial for you and how much you should take daily.

The primary food source of L-citrulline is watermelon. The name L-citrulline comes from Citrullus lanatus, the scientific name for watermelon. Watermelon may contain 0.7-3.6 milligrams of L-citrulline per gram of fruit—or 365 milligrams per cup. Watermelon juice is also a source of L-citrulline.

Other melons and food products, such as cantaloupe, pumpkin, and cucumber, may also contain L-citrulline. However, watermelon is the most studied and most common source.

L-citrulline is available in supplement form as a powder or capsule. L-citrulline supplements are available in two forms: citrulline and citrulline malate.

Citrulline malate contains malic acid, which may help with cellular energy and improve how well your body absorbs the L-citrulline. Citrulline malate is 56.64% citrulline, meaning 1,000 milligrams of citrulline malate provides 566 milligrams. Studies have not determined if one type of citrulline is better.

In studies, L-citrulline has safely been used in doses of 1.5-6 grams daily for up to two months. One-time doses of 15 grams have also been used. L-citrulline does not generally have many side effects. The most commonly reported side effects are stomach discomfort and heartburn.

Interactions

Drugs that may interact with L-citrulline include:

• Blood pressure-lowering medications and supplements: Taking L-citrulline with medications used to treat high blood pressure can lead to hypotension—dangerously low blood pressure. Examples of blood pressure medications include lisinopril, Lopressor (metoprolol), and Aldactone (spironolactone).
• Phosphodiesterase-5 (PDE-5) inhibitors: Taking L-citrulline with PDE-5 inhibitors can also lead to low blood pressure and blood vessel vasodilation. PDE-5 inhibitors are used to treat erectile dysfunction (ED) or pulmonary hypertension. Examples include Viagra (sildenafil) and Cialis (tadalafil).

L-citrulline is an amino acid that may help improve exercise performance, blood pressure, and blood sugar levels.

Talk with your healthcare provider if you are interested in taking L-citrulline. They can help you determine if the supplement would be useful for you and your health conditions.