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L-citrulline: what it does for exercise and blood flow

By the Life in Good Form editors. Updated 2026-10-15.

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What L-citrulline is

Citrulline is a non-essential amino acid and a precursor to nitric oxide, according to a 2026 review in BMC Women's Health. A 2023 meta-analysis explains it is thought to help exercise by boosting nitric oxide production and buffering ammonia. Several studies tested watermelon products as a citrulline source.

Supplements come as L-citrulline or citrulline malate, the form tested in many exercise trials.

What the research shows

Exercise. A 2026 meta-analysis in Nutrients pooled 30 trials with 644 people and found citrulline malate gave a small improvement in overall performance, with no significant change in perceived effort. Reliable dosing and timing have not been established. A 2023 meta-analysis of 9 studies with 158 young adults found no significant effect on endurance.

Blood vessels. A 2025 meta-analysis of 8 trials with 176 middle-aged and older adults found L-citrulline significantly improved flow-mediated dilation, though not overall pulse wave velocity.

Blood pressure findings

• Cold exposure. A 2026 meta-analysis of 6 trials with 162 people found L-citrulline reduced cold-induced systolic blood pressure by about 9.28 mmHg.
• Postmenopausal women. A 2026 review of 12 trials with 360 women aged 50 to 75, lasting 4 to 8 weeks, found most of the 7 blood pressure studies showed lower systolic and mean arterial pressure. Arterial stiffness results were mixed, and two of four studies found better artery function.

In the cold-exposure trials, 87 people took citrulline and 75 served as controls, and brachial systolic pressure fell by about 8.74 mmHg. All 12 postmenopausal trials were run in the United States, and two studies looked at muscle function. The arterial stiffness analysis also found a significant drop in brachial-ankle pulse wave velocity in a subgroup, which the authors said may be useful for heart disease prevention, pending more research.

These are small, short studies. Citrulline is not a replacement for blood pressure treatment.

Why the exercise evidence is weak

• Small, uncertain effect. The 2026 citrulline malate analysis combined 138 effect sizes, but prediction intervals were wide, statistical power was limited and certainty was rated low to very low.
• One-off doses vs daily use. Results looked more stable for a single dose before exercise than for daily use, but the difference was uncertain.
• Specific tasks. Possible benefits for aerobic endurance and short, intense efforts in single-dose studies did not hold up in sensitivity checks.
• No clear best user. Results did not differ by sex, training status, dose or timing.
• Endurance. The 2023 analysis looked at five time-to-exhaustion and four time-to-completion studies, with no meaningful effect in either.

The authors called for larger trials using supplements with verified contents.

Safety

• Blood pressure medicines and nitrates. NOW Foods advises consulting a physician if you take blood pressure medicines, nitrates or other vasodilating drugs, or have abnormal blood pressure.
• Pregnancy. NOW Foods advises a physician check if pregnant or nursing.
• Uncertain dosing. The 2026 exercise meta-analysis said reliable dosing has not been established.

How to choose an L-citrulline supplement

• L-citrulline vs citrulline malate. Check which form and how much citrulline itself is in a serving.
• Pure powder. NOW Foods' L-Citrulline Pure Powder gives 1.5 g (1,500 mg) per half teaspoon, 1 to 2 times daily between meals, with no other ingredients.
• Capsules and tablets. Capsules and tablets are also sold; check the serving size.
• Blends. Some products combine citrulline with arginine or other ingredients. Read every ingredient.
• Expectations. Effects on exercise are small at best.

What to look for when you buy

Questions people ask

What does L-citrulline do?

It helps the body make nitric oxide, which relaxes blood vessels. Studies show small exercise effects and some blood vessel benefits.

Does L-citrulline improve workouts?

A 2026 meta-analysis found only a small improvement with citrulline malate, and endurance did not improve in another analysis.

Does L-citrulline lower blood pressure?

Some studies show lower systolic pressure, especially during cold exposure and in postmenopausal women.

How much L-citrulline should I take?

Follow the label. NOW Foods directs half a teaspoon (1.5 g) 1 to 2 times daily between meals.

Is L-citrulline safe with blood pressure medicine?

Ask your doctor first. NOW Foods flags blood pressure medicines, nitrates and other vasodilators.

Sources

• Effects of Citrulline Malate Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-Analysis (pmc.ncbi.nlm.nih.gov), Nutrients (PMC13304508)
• Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis (pmc.ncbi.nlm.nih.gov), Journal of the International Society of Sports Nutrition (PMC10167868)
• Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function in middle-aged and older adults (pmc.ncbi.nlm.nih.gov), Frontiers in Nutrition (PMC12658987)
• Effect of L-Citrulline Intake on Blood Pressure in Cold Environments: A Systematic Review and Meta-Analysis (pmc.ncbi.nlm.nih.gov), Food Science and Nutrition (PMC12965904)
• Citrulline supplementation in postmenopausal women: a systematic review (pmc.ncbi.nlm.nih.gov), BMC Women's Health (PMC12918617)
• L-Citrulline Pure Powder (www.nowfoods.com/products/supplements/l-citrulline-pure-powder), NOW Foods

Sources checked 2026-10-15.