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L-Arginine

Evidence Level
Moderate
3 Clinical Trials
3 Documented Benefits
3/5 Evidence Score

L-arginine is an amino acid the body uses to make nitric oxide, which relaxes blood vessel walls. Most of its research was done in people with a diagnosed condition. Pooled trials found oral L-arginine lowered systolic blood pressure by about 5 to 6 mmHg, and improved blood vessel function only in people whose function was low to begin with. In a placebo-controlled trial in 98 men with blood-flow-related erection problems, 6 grams a day for 3 months improved erectile function scores. For exercise, a meta-analysis in healthy adults found only a borderline rise in aerobic capacity (VO2max), and a second analysis reporting larger gains has a published critique of its calculations. It can cause stomach upset. In a trial in people recovering from a heart attack, 9 grams a day was linked to more deaths than placebo, so anyone with heart disease should talk to a doctor first.

Studied Dose Blood pressure trials: 4 to 24 g/day. Erectile function trial: 6 g/day for 3 months. VO2max trials: about 2 to 12 g/day for 1 to 8 weeks. After a heart attack, 9 g/day for 6 months was linked to more deaths than placebo.
Active Compound L-Arginine (free form)

Benefits

Blood pressure and blood vessel function

A meta-analysis of 11 placebo-controlled trials (387 adults, 4 to 24 g a day) found systolic blood pressure fell by about 5.4 mmHg and diastolic by 2.7 mmHg, and a later one of 22 trials found 6.4 and 2.6 mmHg. Blood vessel function (flow-mediated dilation) improved only in people whose function was low at the start. High blood pressure needs a doctor's care.

Supported by Trial 2

Erectile function

In a 3-month placebo-controlled trial in 98 men with blood-flow-related erection problems, 6 g a day improved erectile function scores and penile blood flow. A meta-analysis of 10 trials (540 men with mild to moderate problems, some taking arginine combinations) found better erectile scores than placebo or no treatment, while sexual desire scores did not change. Prescription PDE5 inhibitors worked better than L-arginine alone.

Supported by Trial 1, Trial 2

Aerobic capacity (VO2max)

A meta-analysis of 11 placebo-controlled trials in healthy adults, many of them athletes, taking about 2 to 12 g a day for 1 to 8 weeks found VO2max rose by only 0.07 L/min (95% CI 0.00 to 0.13), a borderline result; 6 of the 11 used arginine salts or blends. Another meta-analysis reporting larger gains drew a published critique of its calculations, so any benefit is uncertain.

Supported by Trial 2, Trial 1

Mechanism of action

1

Nitric Oxide Synthesis

L-arginine is converted into nitric oxide by the enzyme nitric oxide synthase (NOS) in endothelial cells, macrophages, and other tissues. This reaction also produces L-citrulline as a byproduct. Nitric oxide acts as a vasodilator, relaxing smooth muscle cells in blood vessel walls, which improves blood flow and reduces vascular resistance.

2

Vascular Effects

By increasing nitric oxide levels, L-arginine can relax blood vessels, which is the proposed reason for the small blood pressure changes measured in trials. Notably, the pooled trials found improved blood vessel function only in people whose function was already impaired, which fits the idea that there is less to gain when nitric oxide production is already normal. Improved oxygen delivery to tissues has not been shown in the studies cited here.

3

Protein and immune roles

L-arginine is a building block of proteins, and immune cells use it to make nitric oxide. These are normal body roles; taking extra arginine has not been shown in the trials summarized here to change metabolism, recovery or immunity.

Clinical trials

1
L-arginine 6 g a day and erectile function: 3-month placebo-controlled trial
PubMed

Multicenter, double-blind, randomized, placebo-controlled trial of 6 g/day L-arginine for 3 months (Menafra et al. 2022, J Endocrinol Invest)

98 men with blood-flow-related (vasculogenic) erectile dysfunction: 51 on L-arginine, 47 on placebo.

Relative improvements in the IIEF-6 erectile function score and in penile artery peak blood flow were significantly greater than with placebo (p<0.0001). In severe cases, the score improved but blood flow did not. Only 24% of men reached scores consistent with no erectile dysfunction. The study reported no funding; the arginine product (Bioarginina) was made by Farmaceutici Damor, from which the senior author reported occasional consulting fees outside this work. Adverse events, none clinically relevant, occurred in 5.9% on arginine and 4.3% on placebo.

2
L-arginine and blood pressure: dose-response meta-analysis
PubMed

Systematic review and dose-response meta-analysis of 22 randomized placebo-controlled trials (30 effect sizes) of oral L-arginine for at least 4 days (Shiraseb et al. 2022, Adv Nutr)

Adults, with and without high blood pressure, pooled across 22 RCTs.

L-arginine lowered systolic blood pressure by 6.40 mmHg (95% CI 4.05 to 8.74) and diastolic by 2.64 mmHg versus placebo. Effects were seen in normotensive and hypertensive groups, but not at doses above 9 g/day, with trials longer than 24 days, or in obese people. The effective dose for systolic pressure was 4 g/day or more.

3
L-arginine after acute myocardial infarction (VINTAGE MI)
PubMed

Single-center, randomized, double-blind, placebo-controlled trial of L-arginine (goal 3 g three times daily) for 6 months added to standard care (Schulman et al. 2006, JAMA)

153 adults after a first ST-elevation heart attack.

No improvement in vascular stiffness or heart ejection fraction. Six people (8.6%) in the L-arginine group died versus none on placebo (p=0.01), and the safety committee closed enrollment. The authors concluded L-arginine should not be recommended after a heart attack.

Side effects and drug interactions

Common Potential side effects

Digestive upset: nausea, vomiting or diarrhea. A review of arginine trials found single doses of 3 to 6 g rarely caused symptoms, while most side effects occurred at single doses above 9 g and eased when the daily amount was split into smaller doses. In pooled erectile function trials, side effects occurred in 8.3% on arginine versus 2.3% on placebo, none severe.
Low Blood Pressure: pooled trials found L-arginine lowered systolic blood pressure by about 5 to 6 mmHg, so people taking blood pressure medicine or who tend to have low blood pressure should check with a doctor first.
High potassium: arginine hydrochloride given by intravenous infusion caused life-threatening high potassium in two people with severe liver disease and moderately reduced kidney function who had also recently taken spironolactone; one died of a heart rhythm problem. The authors advise caution with arginine in kidney or liver disease. Oral supplements were not tested in that report.
Post-Heart Attack Risk: In a randomized trial in 153 people recovering from a heart attack (VINTAGE MI), 6 people taking L-arginine (goal 9 grams a day) died compared with none taking placebo, and the safety committee closed enrollment. Do not take L-arginine after a heart attack unless a doctor tells you to.

Important Drug interactions

Erectile dysfunction medicines (sildenafil, tadalafil, vardenafil): both act on the nitric oxide pathway and may add to blood pressure lowering. In pooled trials the combination did not raise side effects compared with the drug alone, but combine them only with a doctor's advice.
Blood pressure medicines: pooled trials found L-arginine lowered systolic blood pressure by about 5 to 6 mmHg, so the effects may add up; monitor blood pressure.
Blood thinners and antiplatelet medicines (warfarin, aspirin): in a randomized crossover trial in 12 healthy young men, 7 g of L-arginine three times a day (21 g a day) for 3 days markedly reduced platelet clumping in lab tests of their blood (aggregation to ADP was 37% versus 81% on placebo), through the nitric oxide pathway. That dose is far above the 6 g a day used in the erectile function trial, and combined use with these medicines has not been tested; ask a doctor before combining.

Standardized & branded forms of L-Arginine

Trademarked forms of L-Arginine with their own profiles on NutraSmarts. Results from one branded form do not automatically carry over to another, so check each profile for the studies run on that specific product:

Cardiovascular
PepForm® Arginine Peptides (L-Arginine — Glanbia Nutritionals)
PepForm® Arginine Peptides bind free L-arginine to whey-derived peptides, improving the so…

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Frequently asked questions about L-Arginine

Do higher doses of L-arginine work better?

Not clearly. In a dose-response analysis of 22 blood pressure trials, 4 g a day or more lowered systolic pressure, but doses above 9 g a day showed no significant change. A review of side effects found most digestive problems at single doses above 9 g, and fewer when the day's amount was split. The erectile function trial used 6 g a day.

What is L-arginine used for?

L-arginine is an amino acid the body turns into nitric oxide, which relaxes blood vessels. Most research was done in people with a diagnosed condition: pooled trials on blood pressure, on impaired blood vessel function and on erectile dysfunction, plus a review in pregnancy that found less pre-eclampsia but rated the evidence low certainty. Pre-eclampsia is a serious pregnancy complication, so pregnant women should use arginine only if their obstetrician advises it.

Who should avoid L-arginine?

People recovering from a heart attack: in a trial after a first heart attack, 6 people taking L-arginine died versus none on placebo, and enrollment was closed. People with kidney or liver problems should ask a doctor, because arginine given by intravenous infusion caused dangerous high potassium in two patients with severe liver disease and reduced kidney function who had also taken spironolactone. It may also add to blood pressure medicines, and pregnant women should use it only if their obstetrician advises it.

What is L-Arginine?

L-arginine is an amino acid the body uses to make nitric oxide, which relaxes blood vessel walls. Most of its research was done in people with a diagnosed condition.

What is the recommended dosage of L-Arginine?

The clinically studied dose is Blood pressure trials: 4 to 24 g/day. Erectile function trial: 6 g/day for 3 months. VO2max trials: about 2 to 12 g/day for 1 to 8 weeks. After a heart attack, 9 g/day for 6 months was linked to more deaths than placebo. Always follow the product label and check with a healthcare provider for personal advice.

Is L-Arginine safe, and does it have side effects?

Side effects and cautions reported for L-Arginine include: Digestive upset: nausea, vomiting or diarrhea. A review of arginine trials found single doses of 3 to 6 g rarely caused symptoms, while most side effects occurred at single doses above 9 g and eased when the daily amount was split into smaller doses. It may also interact with some medications. L-Arginine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does L-Arginine interact with any medications?

Possible interactions include: Erectile dysfunction medicines (sildenafil, tadalafil, vardenafil): both act on the nitric oxide pathway and may add to blood pressure lowering. In pooled trials the combination did not raise side effects compared with the drug alone, but combine them only with a doctor's advice. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for L-Arginine?

NutraSmarts rates the evidence for L-Arginine as Moderate (3 out of 5). It is backed by 3 study summaries and 14 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(14 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Dong JY, Qin LQ, Zhang Z, Zhao Y, Wang J, Arigoni F, Zhang W. Effect of oral L-arginine supplementation on blood pressure: a meta-analysis of randomized, double-blind, placebo-controlled trials. Am Heart J. 2011;162(6):959-65. doi: 10.1016/j.ahj.2011.09.012.PubMedUsed to support: Meta-analysis of 11 randomized double-blind placebo-controlled trials (387 adults, 4 to 24 g/day): oral L-arginine lowered systolic blood pressure by 5.39 mmHg and diastolic by 2.66 mmHg versus placebo.
  2. Bai Y, Sun L, Yang T, Sun K, Chen J, Hui R. Increase in fasting vascular endothelial function after short-term oral L-arginine is effective when baseline flow-mediated dilation is low: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2009;89(1):77-84. doi: 10.3945/ajcn.2008.26544.PubMedUsed to support: Meta-analysis of randomized placebo-controlled trials (12 short-term studies, 492 participants): oral L-arginine raised flow-mediated dilation by 1.98% overall, but only when baseline FMD was below 7%; there was no effect when baseline FMD was above 7%.
  3. Xu Z, Liu C, Liu S, Zhou Z. Comparison of efficacy and safety of daily oral L-arginine and PDE5Is alone or combination in treating erectile dysfunction: A systematic review and meta-analysis of randomised controlled trials. Andrologia. 2021;53(4):e14007. doi: 10.1111/and.14007.PubMedUsed to support: Meta-analysis of 4 randomized trials (373 men with erectile dysfunction): erectile function improved from baseline with L-arginine, PDE5 inhibitors or both; the combination beat either alone, and PDE5 inhibitors alone beat L-arginine alone. The combination did not increase side effects versus PDE5 inhibitors.
  4. Makama M, McDougall ARA, Cao J, Mills K, Nguyen PY, Hastie R, Ammerdorffer A, Gülmezoglu AM, Vogel JP. L-Arginine and L-Citrulline for Prevention and Treatment of Pre-Eclampsia: A Systematic Review and Meta-Analysis. BJOG. 2025;132(6):698-708. doi: 10.1111/1471-0528.18070.PubMedUsed to support: Systematic review of 20 RCTs (2,028 pregnant women): in prevention trials L-arginine was linked to less pre-eclampsia (RR 0.52) and severe pre-eclampsia (RR 0.23), both low-certainty evidence; 8 RCTs had high risk of bias. The authors call for more trials before clinical use.
  5. Rezaei S, Gholamalizadeh M, Tabrizi R, Nowrouzi-Sohrabi P, Rastgoo S, Doaei S. The effect of L-arginine supplementation on maximal oxygen uptake: A systematic review and meta-analysis. Physiol Rep. 2021;9(3):e14739. doi: 10.14814/phy2.14739.PubMedUsed to support: Meta-analysis of 11 placebo-controlled trials in healthy people (about 2 to 12 g/day for 1 to 8 weeks): arginine raised VO2max by 0.07 L/min (95% CI 0.00 to 0.13, p=0.047), a borderline result; the subgroup using L-arginine alone showed 0.11 L/min. The authors say further studies are needed to confirm it.
  6. Viribay A, Burgos J, Fernández-Landa J, Seco-Calvo J, Mielgo-Ayuso J. Effects of Arginine Supplementation on Athletic Performance Based on Energy Metabolism: A Systematic Review and Meta-Analysis. Nutrients. 2020;12(5):1300. doi: 10.3390/nu12051300.PubMedUsed to support: Meta-analysis pooling 15 placebo-controlled studies reported improvements in aerobic (SMD 0.84, I2 89%) and anaerobic (SMD 0.24) performance tests with arginine. Its calculations were later disputed in a published comment (PMID 40733000), so these effect sizes may be overstated.
  7. Trexler ET. Common Errors in Sports Nutrition Meta-Analyses Lead to Distortion of Pooled Effect Estimates. Comment on Viribay et al. Effects of Arginine Supplementation on Athletic Performance Based on Energy Metabolism: A Systematic Review and Meta-Analysis. Nutrients 2020, 12, 1300. Nutrients. 2025;17(14):2375. doi: 10.3390/nu17142375.PubMedUsed to support: Published comment arguing that the arginine performance meta-analysis (PMID 32370176) included outliers likely caused by treating standard errors as standard deviations, combined different effect-size methods, and counted dependent effect sizes as independent, and that removing the outliers dramatically alters the pooled estimate. The original authors published a reply (PMID 40733001).
  8. Menafra D, de Angelis C, Garifalos F, Mazzella M, Galdiero G, Piscopo M, Castoro M, Verde N, Pivonello C, Simeoli C, Auriemma RS, Colao A, Pivonello R. Long-term high-dose L-arginine supplementation in patients with vasculogenic erectile dysfunction: a multicentre, double-blind, randomized, placebo-controlled clinical trial. J Endocrinol Invest. 2022;45(5):941-961. doi: 10.1007/s40618-021-01704-3.PubMedUsed to support: Randomized placebo-controlled trial in 98 men with vasculogenic erectile dysfunction: 6 g/day L-arginine for 3 months improved IIEF-6 scores and penile peak systolic velocity significantly more than placebo; in severe cases only the score improved. No funding was received; the arginine product came from Farmaceutici Damor, from which the senior author reported occasional consulting fees outside this work.
  9. Shiraseb F, Asbaghi O, Bagheri R, Wong A, Figueroa A, Mirzaei K. Effect of l-Arginine Supplementation on Blood Pressure in Adults: A Systematic Review and Dose-Response Meta-analysis of Randomized Clinical Trials. Adv Nutr. 2022;13(4):1226-1242. doi: 10.1093/advances/nmab155.PubMedUsed to support: Dose-response meta-analysis of 22 RCTs: oral L-arginine lowered systolic blood pressure by 6.40 mmHg and diastolic by 2.64 mmHg versus placebo, with no significant effect at doses above 9 g/day or in trials longer than 24 days.
  10. Schulman SP, Becker LC, Kass DA, Champion HC, Terrin ML, Forman S, Ernst KV, Kelemen MD, Townsend SN, Capriotti A, Hare JM, Gerstenblith G. L-arginine therapy in acute myocardial infarction: the Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) randomized clinical trial. JAMA. 2006;295(1):58-64. doi: 10.1001/jama.295.1.58.PubMedUsed to support: Randomized placebo-controlled trial in 153 people after a first ST-elevation heart attack: L-arginine (goal 9 g/day) for 6 months did not improve vascular stiffness or ejection fraction, and 6 deaths occurred on L-arginine versus none on placebo (p=0.01), so enrollment was closed.
  11. Rhim HC, Kim MS, Park YJ, Choi WS, Park HK, Kim HG, Kim A, Paick SH. The Potential Role of Arginine Supplements on Erectile Dysfunction: A Systemic Review and Meta-Analysis. J Sex Med. 2019;16(2):223-234. doi: 10.1016/j.jsxm.2018.12.002.PubMedUsed to support: Systematic review and meta-analysis of 10 randomized controlled trials (540 men with mild to moderate erectile dysfunction): arginine supplements at 1,500 to 5,000 mg a day, alone or combined with other substances, improved erectile function versus placebo or no treatment (odds ratio 3.37, 95% CI 1.29 to 8.77). IIEF satisfaction, orgasmic and erectile scores improved, but the sexual desire score did not change. Side effects occurred in 8.3% on arginine versus 2.3% on placebo, none severe.
  12. Adams MR, Forsyth CJ, Jessup W, Robinson J, Celermajer DS. Oral L-arginine inhibits platelet aggregation but does not enhance endothelium-dependent dilation in healthy young men. J Am Coll Cardiol. 1995;26(4):1054-61. doi: 10.1016/0735-1097(95)00257-9.PubMedUsed to support: Double-blind randomized crossover trial in 12 healthy men aged 27 to 37 taking 7 g L-arginine three times daily or placebo for 3 days: plasma arginine rose and ADP-induced platelet aggregation was markedly impaired via the nitric oxide pathway, with higher platelet cGMP; blood pressure, heart rate, lipids and flow-mediated dilation did not change.
  13. Grimble GK. Adverse gastrointestinal effects of arginine and related amino acids. J Nutr. 2007;137(6 Suppl 2):1693S-1701S. doi: 10.1093/jn/137.6.1693S.PubMedUsed to support: Review of gastrointestinal adverse effects of arginine and related amino acids: single doses of 3 to 6 g rarely provoked side effects; most side effects (nausea, vomiting, diarrhea) occurred at single doses above 9 g, often within regimens of about 30 g/day or more, and seemed to disappear when doses were divided. Arginine raises nitric oxide in the gut, which can drive fluid secretion.
  14. Bushinsky DA, Gennari FJ. Life-threatening hyperkalemia induced by arginine. Ann Intern Med. 1978;89(5 Pt 1):632-4. doi: 10.7326/0003-4819-89-5-632.PubMedUsed to support: Case report: marked hyperkalemia during and after intravenous arginine monohydrochloride infusion in two patients with severe liver disease and moderate kidney insufficiency who had both received brief courses of spironolactone beforehand, one with a fatal arrhythmia; arginine shifts potassium out of cells, and the authors advise caution in kidney or liver insufficiency. Not an oral supplement study.