NutriFactGuide | Evidence-based supplement and nutrition guide

Medical disclaimer: This article is for education only and is not medical advice. Supplements can interact with medicines and may not suit people with certain health conditions. Talk to a doctor or pharmacist before starting L-arginine, especially if you have heart, kidney or liver disease, asthma, diabetes or low blood pressure, are pregnant, or take regular medication.

Key takeaways

• L-arginine is a semi-essential amino acid. Healthy adults make some of it and get more from protein-rich foods such as meat, fish, dairy, nuts and legumes.

• It is the raw material the body uses to make nitric oxide (NO), a molecule that relaxes blood vessels. That is why most research focuses on blood pressure, circulation, erectile function and exercise.

• The best-supported effect is a modest lowering of blood pressure. Evidence for erectile dysfunction and athletic performance is mixed and mostly from small trials.

• Doses in studies range from about 1.5 g to 24 g per day, and side effects (nausea, bloating, diarrhea) rise with higher doses.

• L-arginine should not be used after a heart attack. A 2006 trial was stopped early after deaths occurred in the arginine group [13].

• In the US, the only FDA-labeled arginine product is an intravenous diagnostic test for growth hormone, not a treatment [2]. Oral L-arginine supplements are not FDA-approved to treat any disease.

What is L-arginine?

L-arginine (often written as arginine or L-Arg) is one of the amino acids that build proteins. Mayo Clinic notes that the body usually makes all the L-arginine it needs [1]. It is classed as "semi-essential" or "conditionally essential," because production may not keep up during illness, injury or rapid growth, when dietary intake or supplementation can matter more.

Beyond building protein, L-arginine has several roles:

• Nitric oxide production. Enzymes called nitric oxide synthases convert arginine into NO. NO signals the smooth muscle in blood vessel walls to relax, widening vessels and improving blood flow.

• Urea cycle. Arginine helps the body clear ammonia, a waste product of protein breakdown.

• Hormone and immune roles. It takes part in the release of hormones such as growth hormone and insulin and supports some immune cell functions.

• Creatine synthesis. Arginine is one building block of creatine, which supplies energy to muscle.

Sources of L-arginine

Food sources

Most people consume arginine every day through protein. Common sources include:

• Animal foods: beef, pork, chicken, turkey, fish and dairy products

• Plant foods: nuts and nut butters (peanuts, almonds, walnuts), seeds, legumes such as lentils, chickpeas and beans, and soy products

• Others: whole grains and dark chocolate in smaller amounts

A varied diet that includes adequate protein usually covers everyday needs. Food sources alone may fall short of the amounts used in supplement trials, which is one reason supplements are studied [15].

Supplement forms

L-arginine supplements are sold as:

• Capsules, tablets and powders (L-arginine free form, often 500 mg to 1,000 mg per capsule)

• Arginine hydrochloride and arginine alpha-ketoglutarate variants

• Drinks and pre-workout blends

• Combination products, often with citrulline, Pycnogenol (pine bark extract), ginseng or vitamins

Citrulline is a related amino acid that the body converts to arginine, and it is sometimes used in place of arginine. Combination products make it hard to tell which ingredient is responsible for any effect, so single-ingredient products are easier to evaluate.

Regulation

In the US, dietary supplements are not approved by the FDA before sale, and the FDA does not check their safety or effectiveness in advance [15]. Quality varies between brands, so independent third-party testing (for example, seals from USP or NSF) is a useful signal.

Uses and effects of L-arginine

1. Blood pressure

This is the most consistent finding. A meta-analysis of 11 randomized, double-blind, placebo-controlled trials with 387 participants found that oral L-arginine at 4 to 24 g per day significantly lowered both systolic and diastolic blood pressure. The authors called for larger, longer trials, especially in people with hypertension [5]. The average reductions were modest, roughly 5 mmHg systolic and 3 mmHg diastolic.

A later dose-response meta-analysis of 22 trials in Advances in Nutrition (2021) also found a significant reduction in systolic pressure. It suggested that lower doses (9 g per day or less) taken for a short period were more effective than higher doses for longer periods, and that diastolic pressure did not fall significantly at doses above 9 g per day [6].

What this means: L-arginine may nudge blood pressure down a little, but it is not a replacement for blood pressure medicine. It can also add to the effect of those medicines, which matters for safety (see below).

2. Erectile dysfunction

Because erections depend on nitric oxide, arginine has been tested for erectile dysfunction (ED) for decades. Results vary:

• In a 1999 randomized trial of 50 men with organic ED, 5 g per day for six weeks led to subjective improvement in 9 of 29 men on arginine (31%) versus 2 of 17 on placebo. All responders had low baseline NO metabolites, and objective penile blood flow did not change [8].

• A 1999 crossover trial of 32 men found that 1.5 g per day (3 x 500 mg) was not better than placebo [9].

• A 2022 multicentre, double-blind, placebo-controlled trial gave 6 g per day for three months to men with vasculogenic ED. Erectile function scores (IIEF-6) improved in the arginine group but not the placebo group, with clearer benefit in mild-to-moderate cases [10].

• A 2019 meta-analysis concluded that 1.5 to 5 g per day improved ED compared with placebo (odds ratio 3.37, 95% CI 1.29 to 8.77) and supported its use in mild-to-moderate ED [11].

• A 2021 meta-analysis found PDE5 inhibitors such as sildenafil worked better than L-arginine alone, and that combining both gave greater improvement than either alone without clearly more side effects [12].

What this means: L-arginine may help some men with mild-to-moderate ED, but it is not as effective as prescription medicine. See our full comparison article on sildenafil vs L-arginine for details.

3. Exercise and athletic performance

Athletes use arginine in pre-workout products on the theory that more NO improves blood flow to muscle. A 2020 systematic review and meta-analysis in Nutrients covering 18 studies (15 in the meta-analysis) concluded that arginine can positively affect aerobic and anaerobic performance. The authors proposed 1.5 to 2 g per day for 4 to 7 weeks for aerobic performance and 10 to 12 g per day for 8 weeks for anaerobic performance [7]. Results across studies are not uniform, many trials are small, and effects in well-trained athletes appear weaker than in less trained people.

4. Blood sugar and type 2 diabetes

Because arginine can influence insulin release, it has been studied in type 2 diabetes. One small double-blind trial of 80 men with type 2 diabetes and mild-to-moderate ED reported that 5 g per day for four weeks improved erectile function and some other sexual function measures compared with placebo [14]. Mayo Clinic also warns that L-arginine might lower blood sugar, so people on diabetes drugs may need their dose adjusted [1]. Larger trials are needed before arginine could be considered for diabetes management.

5. Pregnancy-related high blood pressure

Mayo Clinic notes that some research suggests oral L-arginine might help prevent preeclampsia in pregnant women, and that intravenous infusions may lower blood pressure in women with this complication [1]. This should only be considered under obstetric supervision, because pregnancy safety data for supplements are limited.

6. Medical diagnostic use (FDA-labeled)

The one FDA-labeled arginine product is R-Gene 10, an intravenous arginine hydrochloride solution. The label states that it is indicated as an intravenous stimulant to the pituitary for the release of human growth hormone, where measuring pituitary reserve is useful for diagnosis. The label also states that R-Gene 10 is a diagnostic aid and is not intended for therapeutic use. The recommended adult dose is 30 g of arginine hydrochloride given by infusion over 30 minutes [2]. This is a clinical test, not a supplement use.

Other claimed benefits

Supplement marketing often claims that arginine boosts muscle growth, speeds wound healing, improves immunity, lifts testosterone or treats heart disease. These claims are either poorly supported in healthy people or, in the case of heart disease, contradicted by the safety signals discussed below. Treat them with caution.

How much L-arginine is used?

There is no official recommended daily allowance for L-arginine. Doses reported in research include:

Purpose Doses reported in studies Typical duration

Blood pressure 4-24 g/day (analysis of 11 trials) [5] Weeks

Erectile dysfunction 1.5-6 g/day [8, 9, 10, 11] 2 weeks to 3 months

Aerobic performance 1.5-2 g/day [7] 4-7 weeks

Anaerobic performance 10-12 g/day [7] About 8 weeks

These are research doses, not recommendations. Splitting the total across the day is common in trials and tends to make it easier on the stomach.

Side effects of L-arginine

Mayo Clinic describes oral L-arginine as generally considered safe for most people, but lists possible effects including nausea, abdominal pain, diarrhea, bloating, gout, headache, allergic response, and airway inflammation or worsening of asthma [1].

Dose-related stomach and body effects

A PubMed-indexed dose-response study gave 12 healthy volunteers L-arginine for one-week periods at 3, 9, 21 and 30 g per day. Ten participants reported adverse effects at the first 21 g or 30 g dose (five at each), and the authors concluded that 9 g per day was associated with minimal adverse effects while still raising circulating arginine. They also noted that responses varied widely between individuals [3]. This is a small study, but it matches the general pattern that stomach upset becomes more common with large single doses.

Safety ceiling for healthy adults

In a 2008 risk assessment in Regulatory Toxicology and Pharmacology, Shao and Hathcock found no systematic pattern of adverse effects in human trials, so they used an "observed safe level" approach rather than a formal upper limit. They identified 20 g per day as the observed safe level for healthy adults, and stated that data above that level were not sufficient to confirm long-term safety [4]. Note that the authors worked for an industry trade group (the Council for Responsible Nutrition), and that observed safe levels apply to healthy adults, not to people with medical conditions.

Low blood pressure and dizziness

Because arginine can lower blood pressure, it may cause lightheadedness, fainting or falls in people who already have low blood pressure or who take blood pressure drugs [1, 5].

Asthma and allergy

Mayo Clinic states that L-arginine can worsen allergies or asthma and should be used with caution in these conditions [1].

Herpes (cold sores and genital herpes)

Mayo Clinic advises caution for people with a history of cold sores or genital herpes, because high arginine levels may potentially trigger the virus [1].

Gout

Gout is listed among possible effects of oral L-arginine by Mayo Clinic [1]. People with gout should discuss it with a doctor first.

Heart attack: the most serious warning

The VINTAGE MI trial, published in JAMA in 2006, gave L-arginine (goal of 3 g three times a day) or placebo for six months to 153 people after a first ST-elevation heart attack. L-arginine did not reduce vascular stiffness or improve heart function. Six people in the arginine group died versus none on placebo, and the safety committee closed enrollment. The authors concluded that L-arginine should not be recommended after an acute myocardial infarction [13]. Mayo Clinic also lists recent heart attack as a reason to avoid it [1].

Drug and supplement interactions

According to Mayo Clinic, L-arginine may interact with the following [1]:

Medicine or supplement group Possible problem

Blood pressure drugs, herbs and supplements Additive blood pressure lowering; dizziness or fainting

Anticoagulants and antiplatelet drugs
(such as warfarin, aspirin) Possible increased risk of bleeding

Diabetes drugs Blood sugar may drop further; dose changes may be needed

Potassium-sparing diuretics
(amiloride, spironolactone, triamterene) Mayo advises not to combine them with L- arginine

Nitrates and ED drugs such as sildenafil Additive blood pressure lowering; talk to a doctor first

Always tell your pharmacist about any supplement you take.

Who should avoid L-arginine or ask a doctor first

• Anyone who has had a recent heart attack or has heart disease

• People with low blood pressure or on blood pressure, nitrate, diabetes, anticoagulant or antiplatelet drugs

• People with asthma or allergies, gout, or a history of herpes outbreaks

• Those with kidney or liver disease

• Pregnant or breastfeeding women, and children, unless a doctor recommends it

• People scheduled for surgery should ask their surgeon, as arginine can affect blood pressure and clotting

How to use supplements more safely

1. Start with food. Include protein sources such as fish, poultry, legumes and nuts.

2. Check with a clinician if you have any condition or take any medicine listed above.

3. Choose single-ingredient products with third-party testing, and avoid "male enhancement" or "proprietary blend" formulas that hide amounts.

4. Start low and split doses to reduce stomach upset.

5. Stop and seek care for fainting, chest pain, breathing difficulty, severe diarrhea or an allergic reaction.

6. Do not use it as a replacement for prescribed treatment for blood pressure, diabetes or erectile dysfunction.

Frequently asked questions

Is L-arginine the same as nitric oxide? No. L-arginine is a building block the body uses to make nitric oxide. Taking it does not guarantee higher NO levels, because absorption varies and much oral arginine is broken down before it circulates.

Can L-arginine replace Viagra? Not reliably. Trials show some benefit in mild-to-moderate ED, but a 2021 meta-analysis found PDE5 inhibitors worked better than arginine alone [12].

Is it safe to take every day? Research trials have used daily doses for weeks to months, and an industry-authored risk assessment considers up to 20 g per day an observed safe level for healthy adults [4]. Long-term safety data are limited, and safety depends on your health and medicines.

Does it lower blood pressure? On average, a little [5, 6]. That is why people on blood pressure treatment should be careful.

The bottom line

L-arginine is a natural amino acid with a plausible mechanism, some supportive evidence for modest blood pressure reduction, and mixed evidence for erectile function and exercise. It is generally well tolerated at moderate doses, but higher doses cause stomach upset, it can interact with common medicines, and it should be avoided after a heart attack. For most healthy people, protein-rich foods supply plenty. If you are considering a supplement for a specific health goal, a clinician can help you decide whether it is appropriate and which dose, if any, makes sense.

References

1. Mayo Clinic. L-arginine: overview, safety and side effects, interactions. https://www.mayoclinic.org/drugs-supplements-l-arginine/art-20364681

2. U.S. FDA (Drugs@FDA). R-Gene 10 (arginine hydrochloride injection, USP) prescribing label. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/016931s031lbl.pdf (current labeling: https://labeling.pfizer.com/ShowLabeling.aspx?id=642)

3. Dose-response study of L-arginine (3, 9, 21 and 30 g/day for one week each) in 12 healthy subjects. PubMed PMID 15350985. https://pubmed.ncbi.nlm.nih.gov/15350985

4. Shao A, Hathcock JN. Risk assessment for the amino acids taurine, L-glutamine and L-arginine. Regul Toxicol Pharmacol. 2008;50(3):376-399. Abstract: https://www.sigmaaldrich.com/AT/de/tech-docs/paper/447084 (trade summary: https://www.nutraingredients.com/Article/2009/09/03/Taurine-safety-highlighted-as-usage-levels-decline)

5. Dong JY, Qin LQ, Zhang Z, et al. 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):959-965. doi:10.1016/j.ahj.2011.09.012. https://pubmed.ncbi.nlm.nih.gov/22137067/

6. Systematic review and dose-response meta-analysis of randomized clinical trials of L-arginine supplementation and blood pressure in adults. Adv Nutr. 2021. https://doi.org/10.1093/advances/nmab155 (summary: https://www.vitafoodsinsights.com/health-categories/l-arginine-supplementation-may-effectively-reduce-blood-pressure)

7. 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. https://pubmed.ncbi.nlm.nih.gov/32370176/

8. Chen J, Wollman Y, Chernichovsky T, et al. Effect of oral administration of high-dose nitric oxide donor L-arginine in men with organic erectile dysfunction: results of a double-blind, randomized, placebo-controlled study. BJU Int. 1999;83(3):269-273. https://pubmed.ncbi.nlm.nih.gov/10233492/

9. Klotz T, Mathers MJ, Braun M, Bloch W, Engelmann U. Effectiveness of oral L-arginine in first-line treatment of erectile dysfunction in a controlled crossover study. Urol Int. 1999;63(4):220-223. https://pubmed.ncbi.nlm.nih.gov/10743698/

10. Menafra D, de Angelis C, Garifalos F, et al. 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. https://link.springer.com/article/10.1007/s40618-021-01704-3 (full text: https://pmc.ncbi.nlm.nih.gov/articles/PMC8995264/)

11. Rhim HC, Kim MS, Park Y-J, et al. The potential role of arginine supplements on erectile dysfunction: a systemic review and meta-analysis. J Sex Med. 2019;16(2):223-234. https://pubmed.ncbi.nlm.nih.gov/30770070/

12. 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. https://pubmed.ncbi.nlm.nih.gov/33587304/

13. Schulman SP, Becker LC, Kass DA, et al. L-arginine therapy in acute myocardial infarction: the VINTAGE MI randomized clinical trial. JAMA. 2006;295(1):58-64. https://pubmed.ncbi.nlm.nih.gov/16391217/ (full text: https://jamanetwork.com/journals/jama/fullarticle/202136)

14. Effect of oral supplementation of L-arginine on sexual function in men with type 2 diabetes: a double-blind clinical trial. https://jnfs.ssu.ac.ir/xml_out.php?a_id=76

15. Medical News Today. L-arginine: benefits, food sources, side effects and interactions (notes on food sources and FDA oversight of supplements). https://www.medicalnewstoday.com/articles/318174