The amino acid known as L-citrulline is made naturally in your body. Research isn’t clear whether these supplements will help boost exercise performance, lower blood pressure, or help with erectile dysfunction.

Experts refer amino acids as the building blocks of proteins. Specific combinations of 20 different amino acids make proteins in your body.

However, there are many other amino acids that are not involved in making proteins. L-citrulline is an example of one such amino acid.

Below, we discuss what L-citrulline is, its potential benefits, and L-citrulline supplementation. Keep reading to discover more.

L-citrulline is a nonessential amino acid, meaning the body already makes it naturally. Glutamine, which is the most abundant amino acid in the body, mainly produces L-citrulline.

Unlike many amino acids you may have heard of, L-citrulline is not used to make proteins. Instead, it has other functions in the body.

L-citrulline is involved in the urea cycle, where toxic ammonia converts into urea. Ammonia is made both by the bacteria in your gut and by your cells when they process protein. Converting ammonia into urea lets the urea pass out of the body in urine.

L-citrulline helps the formation of nitric oxide (NO). NO plays a role in the dilation (expanding) of blood vessels. It also helps release certain hormones, such as the growth hormone and insulin.

L-citrulline has several benefits, which include:

Exercise and athletic performance

One of the main benefits of L-citrulline is that it may enhance exercise or athletic performance. It does this through its effect on nitric oxide (NO) production.

Generation of NO causes the breaking down of an amino acid called arginine into L-citrulline and NO. But L-citrulline is also a precursor to arginine. The body converts about 80% of citrulline into arginine.

Supplementing your body with L-citrulline increases arginine, thus increasing NO levels. Higher NO levels may lead to increased blood flow, which means your tissues receive more oxygen and nutrients.

According to some studies, L-citrulline can help increase oxygen uptake and muscle oxygenation. A 2021 study in rats found that giving L-citrulline by mouth increases the levels of various substances delivered to your muscles.

Small studies found that taking L-citrulline supplements improved performance in aerobic exercise, specifically cycling and weightlifting.

The National Institutes of Health (NIH) states that research in using L-citrulline to boost exercise performance is limited and conflicting. Recent reviews have found that L-citrulline did not show any benefits in aerobic exercise or endurance performance.

Blood pressure

As mentioned earlier, L-citrulline helps in the process of making NO. NO causes the blood vessels to expand. This can help lower your blood pressure.

A 2019 review found that the blood pressure-lowering effects of L-citrulline are not clear. It suggests that L-citrulline may lower systolic blood pressure by 4.1–7.5 mmHg (millimeters of mercury) and diastolic blood pressure by 2.08–3.77 mmHg.

Another 2019 review involved 8 studies where researchers were studying the effects of L-citrulline on blood pressure. They found that L-citrulline supplements at lower doses may reduce systolic blood pressure.

A 2018 research review suggests that L-citrulline supplements did not help reduce blood pressure.

Erectile dysfunction

NO causes the widening of blood vessels, resulting in an increased blood flow, including to the genitals. L-citrulline supplements may help in erectile dysfunction (ED) treatment.

One small 2011 study found that taking 1.5 grams of L-citrulline per day for one month led to improvement in maintaining erection in men with ED.

However, L-citrulline was still less effective than phosphodiesterase type 5 inhibitors, such as sildenafil (Viagra) and tadalafil (Cialis) to treat ED.

Watermelon is the main food source of L-citrulline. The NIH notes that researchers have found that one cup of diced seedless watermelon contains about 365 milligrams of L-citrulline.

L-citrulline concentration can depend on the specific type of watermelon. Research from 2019 notes that L-citrulline levels are high in the Crimson Sweet and Dixielee varieties of watermelon.

Other foods have much lower levels of L-citrulline than watermelon. Some examples of other foods containing L-citrulline include:

L-citrulline is available as a supplement. It often comes in a powder or capsule form.

There’s no standard recommended daily dose of L-citrulline.

The NIH notes that research studies have found that L-citrulline given to nonathletes at 6 grams per day for 4 weeks did not show any adverse effects.

More extensive studies would determine the safety of L-citrulline, particularly when you take it in supplemental form for months at a time.

Older research states that people involved in the study could tolerate up to 15 grams of L-citrulline over a maximum of 8 hours without side effects.

Supplements containing L-citrulline come in two forms: citrulline and citrulline malate. Citrulline malate is 56.64% citrulline. This means that 1 gram of citrulline malate contains a little over 0.5 grams of citrulline.

Studies report a few side effects of L-citrulline supplements. The NIH notes that it is possible for some people taking L-citrulline to experience stomach discomfort.

But studies are not clear on whether these supplementals are safe and effective.

It’s also possible that L-citrulline may interact with some prescription drugs, such as:

However, L-citrulline may interact with some prescription medications, such as medications for hypertension, cardiovascular disease, and ED.

Consider talking with your doctor before starting any new supplement. They can advise you on whether or not a specific supplement is suitable for you.

Your doctor can recommend an L-citrulline dosage that is right for you and also discuss side effects or drug interactions.

L-citrulline is a nonessential amino acid that has a variety of functions in the body. You can take it as a supplement.

L-citrulline supplements may have several health benefits, including boosting exercise performance and lowering blood pressure. However, research into these areas is still limited, and more extensive studies would help us better understand its benefits.

Although research isn’t clear whether L-citrulline is safe, it shows a few side effects associated with L-citrulline. Drug interactions may occur, so talk with your doctor. They will tell you whether L-citrulline supplementation is a good option for you and what dosage you should take.