Medically Reviewed by Melinda Ratini, MS, DO on September 06, 2023
3 min read

L-citrulline is a substance called a non-essential amino acid. Your kidneys change L-citrulline into another amino acid called L-arginine and a chemical called nitric oxide.

These compounds are important to your heart and blood vessel health. They may also boost your immune system.

L-citrulline boosts nitric oxide production in the body. Nitric oxide helps your arteries relax and work better, which improves blood flow throughout your body. This may be helpful for treating or preventing some diseases.

There is some evidence to suggest the supplement could possibly help lower blood pressure in people with elevated blood pressure. Elevated blood pressure raises your risk for high blood pressure and heart disease. Definitions for blood pressure levels are:

  • Normal blood pressure: less than 120 over less than 80(<120/<80)
  • Elevated: 120-129 over less than 80 (120-129/<80)
  • Hypertension stage 1: 130-139 or 80-89
  • Hypertension stage 2: greater than 140 or greater than 90 (≥140 or ≥90).

L-citrulline supplements may ease symptoms of mild-to-moderate erectile dysfunction (ED). Scientists say L-citrulline does not work as well as ED drugs such as Viagra. However, it appears to be a safe option.

Animal studies suggest L-citrulline might also help people with blood vessel problems such as slow wound healing due to diabetes.

Other animal research says L-citrulline might improve muscle protein levels and prevent malnourishment in the elderly.

The animal research also suggests L-citrulline may help treat intestinal problems, including:

Certain genetic disorders and health conditions such as liver disease may be helped by L-citrulline supplements.

Early human studies also hint that L-citrulline may be helpful for Parkinson's disease and certain dementias.

Some people also take L-citrulline to build muscles and improve athletic performance. But research shows it does not help well-trained athletes perform or exercise better.

The supplement usually comes in powder form. The suggested dosage for L-citrulline depends on what disease you are trying to treat or prevent, but is sometimes used up to 6 grams a day for up to 16 days. However, optimal doses of L-citrulline have not been set for any condition. Quality and active ingredients in supplements may vary widely. This makes it hard to set a standard dose.

Yes, watermelon contains L-citrulline.

There are no reported side effects of L-citrulline.

However, the supplement may affect the way certain drugs work in your body. Do not take this supplement if you are taking:

Combining L-citrulline with those drugs may cause a dangerous drop in blood pressure.

You should also be careful when taking L-citrulline if you take any type of blood pressure medicine.

Do not use L-citrulline if you are pregnant or breastfeeding.

Always tell your doctor about any supplements you are taking. That way, your doctor can check on any potential side effects or interactions with any medications.

The U.S. Food and Drug Administration (FDA) regulates dietary supplements; however, it treats them differently from foods and drugs. The manufacturer is responsible for the safety and proper labeling of their products.