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L-arginine

An amino acid in protein-rich foods such as nuts and animal products, which the body also makes. It is sold in supplements for exercise and erections.

Explained simply · Last reviewed

What it is

L-arginine, also called arginine, is an amino acid. The NIH Office of Dietary Supplements (ODS) says it is found in many protein-containing foods, especially animal products and nuts, and that the body also makes it, mainly in the kidneys, from another amino acid called citrulline. ODS explains that the body converts some arginine into nitric oxide, a substance that widens blood vessels and can increase blood flow.

More about L-arginine

The NIH Office of Dietary Supplements (ODS) says it is found in many protein-containing foods, especially animal products and nuts, and that the body also makes it, mainly in the kidneys, from another amino acid called citrulline. ODS explains that the body converts some arginine into nitric oxide, a substance that widens blood vessels and can increase blood flow.

ODS reports that some experts link arginine to exercise through nitric oxide, which can also increase the delivery of oxygen and nutrients to skeletal muscle. ODS covers arginine in its fact sheet on ingredients in supplements "designed or claimed to enhance exercise and athletic performance".

Arginine is also sold in supplements for erections: a 2023 review examined 27 supplements marketed in Italy for erectile dysfunction and found L-arginine in about 63% of them.

Also known as: arginine

At a glance

Safety: known risks and 1 group who should avoid it or take extra care. See Safety ↓

Claims made about L-arginine, and how strong the evidence is for each:

Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate

Safety

Read this before the ratings below.

Risks

  • The NIH Office of Dietary Supplements (ODS) reports that most study results suggest "up to 9 g/day arginine for several days or weeks is safe and well tolerated." It reports that "at doses of 9–30 g/day, the most commonly reported adverse reactions are gastrointestinal discomfort, such as diarrhea and nausea, and slightly reduced blood pressure."
  • ODS states that the safety of taking high-dose arginine supplements for more than 3 months is not known.
  • In a 2006 trial in 153 people after a first heart attack (ST-elevation myocardial infarction), 6 of those taking L-arginine (8.6%) died during the 6-month study, against none of those taking placebo. Five of the six were aged 60 or over, and one died 3 weeks after stopping the study drug. The trial's data and safety monitoring committee recommended stopping enrollment because of the excess deaths in the L-arginine group. The authors note that death was not one of the trial's pre-specified primary outcomes (clinical events, including deaths, were recorded as a secondary outcome), that the excess deaths were "an unexpected safety monitoring concern", and that "the results could be due to (small but nonzero) chance". They agreed with stopping the trial early and concluded that L-arginine should not be given to people after a heart attack. A letter about the trial and the authors' reply were published; this page has not read them.
  • Four trials in a 2022 blood-pressure review reported side effects: increased stool frequency and bloating, diarrhea, indigestion and abdominal pain, and in one trial weakness, skin rash and eosinophilia (a rise in one type of white blood cell). The reviewers say the included trials "revealed no major side effects".
  • In pregnant women at risk of pre-eclampsia, a 2025 review pooled three prevention trials in 328 women: the estimate leaned toward more side effects with L-arginine, but the difference was not statistically significant, and the reviewers rated how sure they can be of that evidence (certainty) as very low. At that certainty, these trials cannot show whether L-arginine causes side effects, and do not show that it does not.
  • In a 2007 trial in people with peripheral artery disease, serious and total adverse events did not differ between L-arginine and placebo, but walking distance improved significantly less with L-arginine. The authors titled their paper "no benefit and possible harm."

Who should avoid it or take extra care

  • People who have just had a heart attack: in people following a first ST-elevation heart attack, the authors of the 2006 trial above concluded that L-arginine "should not be recommended following acute myocardial infarction."

Safety sources: Source [1]Source [2]Source [3]Source [4]Source [5]

What the evidence says

Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.

  • Lowers blood pressure in adults Evidence rating: Limited

    People with high blood pressure take it hoping it will bring their readings down.

    A 2022 review of 22 trials found lower blood pressure with L-arginine but rated that low certainty; in 2011 EFSA judged a cause-and-effect link not established.

    A 2022 meta-analysis pooled 22 placebo-controlled trials in adults, ranging from healthy people to people with various health conditions. It found that L-arginine lowered systolic blood pressure by about 6.4 mmHg and diastolic blood pressure by about 2.6 mmHg on average. The review measured blood pressure itself, not outcomes such as heart attack or stroke.

    The reviewers rated the certainty of both results as low. Results varied widely between trials, and the trials studied people with different conditions. The authors say the effects of longer-term use need further research.

    In 2011 the European Food Safety Authority (EFSA) assessed a proposed health claim for the general population. It noted that one small, short, partially controlled study had observed an effect, while two small longer-term studies had not. It concluded that a cause-and-effect relationship between L-arginine and maintaining normal blood pressure had not been established.

    This rating follows the lowest certainty among the blood-pressure outcomes, which is low.

    Sources: Source [1]Source [2]

  • Improves erectile function in men with erectile dysfunction Evidence rating: Limited

    Men with erection problems take it hoping it will help them get and keep an erection.

    A 2023 review of four trials in 246 men found better erectile function scores, but judged about half the evidence at high risk of bias; in 2011 EFSA found no cause-and-effect link established.

    A 2023 meta-analysis pooled four controlled trials of L-arginine alone, in 246 men. It found improved scores on erectile function questionnaires.

    The review states that it used GRADE to assess the certainty of its evidence, but it reports no certainty rating. The reviewers judged about half of that evidence at high risk of bias and most of the rest unclear. They wrote that they "can only state that the various EIs are potentially effective in improving erectile function on average", EIs being the ingredients the review identified as effective. They call for more trials with more patients.

    In 2011 EFSA assessed a proposed health claim for the general male population. It noted that the two intervention studies it assessed did not show a significant effect on erectile function, and concluded that a cause-and-effect relationship had not been established. Where sources disagree, this page takes the lower rating.

    Sources: Source [1]Source [2]

  • Improves exercise or athletic performance Evidence rating: Limited

    People who work out or play sport take it hoping it will boost their strength, endurance or recovery.

    The NIH Office of Dietary Supplements says arginine's ability to improve exercise performance has little scientific support; a 2020 review reporting improvements is disputed in print.

    The NIH Office of Dietary Supplements (ODS) describes the research on arginine as a performance enhancer as limited and conflicting. Overall, it says, that research suggests arginine has little to no effect on performance in either anaerobic or aerobic exercise. ODS concludes that arginine's ability to enhance strength, improve exercise or athletic performance, or promote muscular recovery "has little scientific support".

    ODS reports that a review of 54 studies in healthy, active adults concluded that arginine, alone or more commonly combined with other ingredients, provided little or no enhancement of athletic performance and did not improve recovery from exhaustion. Most of those studies were small, mainly in young men, and lasted only 4 to 8 weeks.

    A 2020 systematic review of 18 trials, almost all of whose participants were men, pooled 15 of them in a meta-analysis. It reported a small improvement in anaerobic performance tests and a large one in aerobic tests, although the aerobic results varied widely between trials and showed publication bias.

    That analysis has been challenged in print. In a 2025 comment in the same journal, the comment's author argues that three of its aerobic results are outliers, most likely inflated by standard errors being treated as standard deviations, and that removing them "dramatically alters the pooled effect estimate". In a reply, four of the review's five authors write that they "recognize that the points raised are relevant" and that their more recent analyses use more rigorous methods. The reply does not present a corrected analysis of the arginine data. Where sources disagree, this page takes the lower rating.

    Sources: Source [1]Source [2]Source [3]Source [4]

  • Helps prevent pre-eclampsia in pregnant women at high risk Evidence rating: Limited

    Some pregnant women at high risk of pre-eclampsia take it hoping to lower their chance of developing it.

    A 2025 review of four trials in 745 women at high risk found L-arginine may reduce the risk of pre-eclampsia, and rated that evidence low certainty.

    A 2025 meta-analysis looked at L-arginine in women at high risk of pre-eclampsia. From four trials in 745 women, it found that L-arginine may reduce the risk of pre-eclampsia. From three trials in 295 women, it found that it may reduce the risk of severe pre-eclampsia. The reviewers rated both results low certainty.

    For pre-eclampsia, they note that one of the studies was at high risk of bias, that there were few events, and that there were too few studies to test for publication bias. For severe pre-eclampsia, they note risk of bias in the included trials, few events, a wide confidence interval, and again too few studies to test for publication bias.

    In women at risk, the estimate for side effects, from three trials in 328 women, leaned toward more side effects with L-arginine but was not statistically significant, and was rated very low certainty: too little evidence to tell either way. For blood pressure, the estimates were also very low certainty, with wide confidence intervals that included no effect: again too little evidence to tell. In women already diagnosed with pre-eclampsia, none of the trials reported whether the condition progressed to severe pre-eclampsia or eclampsia, and a possible fall in systolic blood pressure was very uncertain.

    The authors say L-arginine may be promising but that the findings should be interpreted cautiously, and call for trials to establish who might benefit, the dose, and when to start. The same review found only one small trial of L-citrulline, in 36 women, which reported no effect on pre-eclampsia or blood pressure. This rating follows the lowest certainty among the pre-eclampsia outcomes, which is low.

    Sources: Source [1]

  • Improves walking in peripheral artery disease Evidence rating: Insufficient

    People with peripheral artery disease take it hoping to walk further before leg pain stops them.

    One 6-month trial in 133 people found walking distance improved significantly less with L-arginine than with placebo; its authors concluded long-term use is not useful.

    No systematic review of L-arginine for peripheral artery disease was found for this page. The authors of the trial described here note that earlier small, short-term studies had reported benefits. Their trial, which they describe as the largest and longest randomized trial of L-arginine's effect on functional capacity, randomized 133 people with leg pain on walking (intermittent claudication) caused by peripheral artery disease to oral L-arginine or placebo for 6 months.

    Walking distance improved in both groups, but significantly less with L-arginine than with placebo. Measures of nitric oxide availability, including blood-vessel function, were no better, and in some cases worse, than with placebo. The authors concluded: "As opposed to its short-term administration, long-term administration of L-arginine is not useful in patients with intermittent claudication and PAD."

    The trial was supported in part by grants from the NIH and from Ajinomoto Inc, which manufactured the study's L-arginine. One author disclosed, in the 2007 paper, consulting for Ajinomoto and United Therapeutics and royalties from Stanford University patents on the nitric oxide synthase pathway. A letter about the trial and the authors' reply were published; this page has not read them.

    Without a review, one trial is too little evidence to rate this claim either way, so it is rated insufficient.

    Sources: Source [1]

Sources

  1. Effect of l-Arginine Supplementation on Blood Pressure in Adults: A Systematic Review and Dose-Response Meta-analysis of Randomized Clinical Trials
    Advances in Nutrition, 2022 · Meta-analysis · Primary source · Certainty: low
  2. Scientific Opinion on the substantiation of health claims related to L-arginine and “immune system functions” (ID 455, 1713), growth or maintenance of muscle mass (ID 456, 1712, 4681), normal red blood cell formation (ID 456, 664, 1443, 1712), maintenance of normal blood pressure (ID 664, 1443), improvement of endothelium-dependent vasodilation (ID 664, 1443, 4680), “physical performance and condition” (ID 1820), “système nerveux” (ID 608), maintenance of normal erectile function (ID 649, 4682), contribution to normal spermatogenesis (ID 650, 4682), “function of the intestinal tract” (ID 740), and maintenance of normal ammonia clearance (ID 4683) pursuant to Article 13(1) of Regulation (EC) No 1924/2006
    EFSA Panel on Dietetic Products, Nutrition and Allergies (EFSA Journal), 2011 · Health authority summary · Primary source
  3. Dietary Supplements for Erectile Dysfunction: Analysis of Marketed Products, Systematic Review, Meta-Analysis and Rational Use
    Nutrients, 2023 · Meta-analysis · Primary source
  4. Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals
    NIH Office of Dietary Supplements, 2024 · Health authority summary · Primary source
  5. Effects of Arginine Supplementation on Athletic Performance Based on Energy Metabolism: A Systematic Review and Meta-Analysis
    Nutrients, 2020 · Meta-analysis · Primary source
  6. 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 · Published comment · Not counted toward ratings
  7. Reply to Trexler, E.T. 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 · Published comment · Not counted toward ratings
  8. L-Arginine and L-Citrulline for Prevention and Treatment of Pre-Eclampsia: A Systematic Review and Meta-Analysis
    BJOG: An International Journal of Obstetrics and Gynaecology, 2025 · Meta-analysis · Primary source · Certainty: very low
  9. L-arginine supplementation in peripheral arterial disease: no benefit and possible harm
    Circulation, 2007 · Randomized controlled trial · Supporting source
    This source discloses industry funding.
    Some of its authors disclose ties to industry.
  10. L-arginine therapy in acute myocardial infarction: the Vascular Interaction With Age in Myocardial Infarction (VINTAGE MI) randomized clinical trial
    JAMA, 2006 · Randomized controlled trial · Supporting source

Page history

Show all 7 changes to this page
  • — Rewritten to the content style guideline; ratings and sources unchanged.
  • — Revised in the source audit, which applied the rule that a source is cited only once its full text has been read. The 2006 heart-attack trial has now been read in full: the safety section adds that five of the six deaths were in people aged 60 or over, that one came 3 weeks after the study drug was stopped, and that the authors say the excess deaths "could be due to (small but nonzero) chance", and no longer says the trial was read only from its abstract. Its funding and author-disclosure fields are updated from its disclosure statements. Two sources whose full text could not be read were removed: the 2019 erectile dysfunction meta-analysis, with its summary sentence and its side-effect figures, and the 2009 heart-attack meta-analysis, with its sentence on deaths. No rating changed.
  • — Published. All five claims, the safety section and every source passed the site's source and wording reviews. Three sources read from their abstracts, and two unread letters on cited trials, stay logged in docs/08-open-decisions.md.
  • — Cited the 2025 published comment on the 2020 exercise meta-analysis and the review authors' reply, both read in full, beside the review they discuss. They are labeled as published comments and do not count toward the rating. No rating changed.
  • — Revised after the second source review and the first wording review. The severe pre-eclampsia certainty reasons no longer give a count of high-risk trials, because the review's own figures and footnote disagree. Side-effect and blood-pressure findings in pregnancy are described as too uncertain to tell either way. The 2009 heart-attack meta-analysis is described as comparing L-arginine with control groups, with a note that its pooled trials could not be identified. The erectile dysfunction and pre-eclampsia headings now match the populations studied. Quotations were checked against the sources and marked as quotations. No rating changed.
  • — Revised after source review. The erectile dysfunction summary now says the 2023 review states it used GRADE but reports no certainty rating. The pre-eclampsia side-effect finding is reported as leaning toward more side effects, not significant and very low certainty, rather than as no association, in both the safety section and the claim. The pre-eclampsia certainty reasons now follow the review's own summary-of-findings table, and a sentence on trial length that contradicted the blood-pressure review's own tables was removed. No rating changed.
  • — First drafted. Blood pressure, erectile dysfunction, exercise performance and pre-eclampsia prevention rated limited; peripheral artery disease rated insufficient.