Citrulline (L-Citrulline): Benefits, Dosage And Side Effects (2024)

L-citrulline is an amino acid—which are fundamental molecules that serve as the building blocks of proteins—that is produced naturally by the body. It’s found in certain food sources and supplements.

Once ingested, L-citrulline is converted into L-arginine, another amino acid that is used to produce nitric oxide, which is a compound that increases blood flow. Though L-arginine supplements are also readily available, research suggests citrulline supplements may actually be more effective at increasing levels of arginine and the production of nitric oxide in the body.

L-citrulline is widely available in supplement form, often in doses ranging from 750 milligrams to 3,000 milligrams per serving. It’s also found naturally in certain food sources, according to Emmy Bright, a registered dietitian and founder of Real Good Nutrition, a private nutrition practice in Madison, Wisconsin.

“The best source of L-citrulline is watermelon, which has up to 3.5 milligrams of the amino acid per gram,” says Bright. L-citrulline is present in other types of melons in smaller amounts as well, including casaba melon, mouse melon and horned melon rind. However, it’s estimated that you would need to consume 2.2 to 3.3 pounds of fresh watermelon per day to obtain 3 grams of citrulline, which is considered the minimum effective dose^[1]Allerton TD, et al. L-Citrulline Supplementation: Impact on Cardiometabolic Health. Nutrients. 2018;10(7):921. . Therefore, most people opt for supplementation instead, thanks to the convenience that it offers.

L-citrulline is linked to several possible health perks. Keep reading for a few of the top benefits, according to experts.

May Improve Erectile Dysfunction

Ryan Sultan, M.D., a New York-based psychiatrist and assistant professor of clinical psychiatry at Columbia University Medical Center, notes that he regularly uses L-citrulline to help treat erectile dysfunction (ED) caused by selective serotonin reuptake inhibitors (SSRIs), a type of antidepressant.

L-citrulline works for this use by promoting the dilation of blood vessels and improving blood flow, notes Dr. Sultan. One small study of 50 men with ED found that L-citrulline combined with other ingredients (including French maritime pine bark, roburins and L-arginine) improved erectile function^[2]Stanislavov R, et al. Improvement of Erectile Function by a Combination of French Maritime Pine Bark and Roburins With Aminoacids. Minerva Urol Nefrol. 2015;67(1):27-32. . Another study found that people with ED had lower levels of L-citrulline. The authors of the study concluded that low levels of L-citrulline and L-arginine could increase the risk of ED by reducing nitric oxide levels^[3]Barassi A, et al. Levels of L-Arginine and L-Citrulline in Patients With Erectile Dysfunction of Different Etiology. Andrology. 2017;5(2):256-261. .

Could Boost Exercise Performance

“Research shows that taking a supplementing dose of L-citrulline before exercise may be effective toward reducing exhaustion and muscle soreness,” says Bright. She explains that it might help increase oxygen uptake by the muscles and notes that it may be more effective for anaerobic exercise (like weightlifting) rather than aerobic activities, such as jogging.

One small 2018 study showed that pairing citrulline and glutathione (an antioxidant) with resistance training improved lean body mass and muscle strength after four weeks compared to a placebo. However, there was no significant difference between either group after eight weeks^[4]Hwang P, et al. Eight Weeks of Resistance Training in Conjunction With Glutathione and L-Citrulline Supplementation Increases Lean Mass and Has No Adverse Effects on Blood Clinical Safety Markers in Resistance-Trained Males. J Int Soc Sports Nutr. 2018;15(1):30. .

Might Help Lower Blood Pressure

Some research suggests that L-citrulline could help reduce blood pressure levels. For instance, one review of eight studies found that supplementing with L-citrulline may reduce systolic blood pressure, and may also decrease diastolic blood pressure when taken in doses of at least 6 grams per day^[5]Barkhidarian B, et al. Effects of L-Citrulline Supplementation on Blood Pressure: A Systematic Review and Meta-Analysis. Avicenna J Phytomed. 2019; 9(1):10–20. .

However, Bright points out that research on the potential blood pressure-lowering benefits of L-citrulline is inconsistent. In fact, another review found that L-citrulline supplementation had no effect on blood pressure levels^[6]Mirenayat MS, et al. Effect of L-Citrulline Supplementation on Blood Pressure: a Systematic Review and Meta-Analysis of Clinical Trials. Curr Hypertens Rep. 2018;20(11):98. . Additionally, Bright notes that more research is needed to understand the effects of L-citrulline on other aspects of heart health, including heart disease and heart failure.

The recommended dosage for L-citrulline might vary depending on why you’re taking it, according to Dr. Sultan. “For exercise performance, doses of 6 to 8 grams per day have been used in research studies,” he explains. “For cardiovascular health and erectile dysfunction, lower doses (around 1.5 to 3 grams per day) have been used.”

Always check in with a doctor before taking L-citrulline. They can provide additional guidance on whether supplementation is right for you and how much you should take each day.

“L-citrulline is generally well-tolerated and side effects are rare, but they can occur,” says Dr. Sultan, explaining that some of the most common side effects include stomach discomfort, heartburn and changes in urination.

Dr. Sultan also notes that L-citrulline may interact with certain medications, including those used to treat high blood pressure or erectile dysfunction, which is why it’s important to talk to a health care provider before starting supplementation.

It’s best to talk to a doctor before turning to supplements to address any health concerns, including high blood pressure or erectile dysfunction. A doctor can help determine the cause and best course of treatment based on your needs, which may include supplements, prescription medications or other lifestyle changes. It’s also important to consult with a doctor before taking supplements if you have any underlying conditions or are taking medications in order to avoid interactions or other adverse effects on health.

While L-citrulline supplements may offer some promising benefits for certain health conditions, they should be paired with a balanced diet, good sleep and a healthy lifestyle to maximize the potential benefits. Enjoying plenty of foods rich in L-citrulline, such as melons, might also be a good option to increase your intake of L-citrulline, along with the many other beneficial nutrients found in these ingredients.