Nitric Oxide
What’s New This Month
- Erectile function: The 98-man trial now has side-effect numbers: 5.88% on arginine versus 4.26% on placebo over 3 months, none judged clinically relevant. A drug company supplied the arginine. 1
- Recalls: Health Canada lists two recalls of citrulline powders for possible milk-protein contact. Our earlier note of no recall was wrong. 2 3
- Correction: FDA’s July 2025 warning letter to Valentine Enterprises names neither citrulline nor arginine, so we no longer count it. 4
- Blood flow: According to Korea’s Ministry of Food and Drug Safety records (translated), L-arginine is recognised for a blood-flow claim at 6 g a day. A permitted claim is not proof, so blood flow stays TBD. 5
Overview
Nitric oxide is a gas the body makes to relax blood vessels. It lasts only seconds, so it cannot be sold as a pill. 6
Supplements instead supply two amino acids, the building blocks of protein. L-arginine is turned into nitric oxide. L-citrulline, or citrulline malate, is turned into arginine in the kidneys. 6
Labels claim better erectile function, lower blood pressure, more blood flow and “pump,” stronger workouts, faster recovery and immune support.
How We Researched It
We rate each marketing claim with a modified version of GRADE, the system medical researchers use to say how sure we can be (i.e., high, moderate, low or very low), and check each trial with the Cochrane risk-of-bias tool, which asks whether a study’s design could skew its results. For nitric oxide boosters we used 32 evidence records, mostly from October 2022 to October 2026. We also checked ten regulators and safety databases, including FDA, Health Canada and Korea’s food safety agency, plus NIH and ConsumerLab.
Research NotesTop three benefits
Erectile Function GRADE: Low
In a 98-man trial, 6 g a day for 3 months raised the median erectile function score from 20 to 24; placebo did not change. Four pooled trials gave a 3.2-point gain. 1 8
Bias check: Half the pooled trials were at high risk of bias and results varied widely. The main trial’s arginine came from a drug company, and we found no funding statement. 8 1
Pairing with ED Medicine GRADE: Low
A review of 15 trials in 1,000 men ranked arginine plus tadalafil above tadalafil alone. It helped men with a physical cause, not those without one. 14
Bias check: It shares trials with the other reviews, and funding is not stated. The drug-interaction warning still stands. 12
Blood Pressure GRADE: Low
Citrulline lowered top blood pressure about 4 points across 15 trials. Arginine did the same on 24-hour monitoring in 5 studies. 13 19
Bias check: Both fall short of the 5-point drop we count as meaningful, and the arginine pool is small.
Benefit Evaluation
| Claim | Claim Verdict | Research Confidence | Supporting Evidence | Safety Risk | Product Quality | FactStack™ Rating |
|---|---|---|---|---|---|---|
| Erectile Function | Promising | Low | Promising | Real Concern | Variable | Caution |
| Pairing with ED Medicine | Promising | Low | Promising | Real Concern | Variable | Caution |
| Blood Pressure | Promising | Low | Promising | Real Concern | Variable | Caution |
| Blood Flow | TBD | Very Low | TBD | Real Concern | Variable | Warning |
| Athletic Performance | TBD | Low | TBD | Real Concern | Variable | Warning |
| Endurance | TBD | Very Low | TBD | Real Concern | Variable | Warning |
| Strength | TBD | Low | TBD | Real Concern | Variable | Warning |
| Recovery | TBD | Very Low | TBD | Real Concern | Variable | Warning |
| Disease Treatment | TBD | Low | TBD | Real Concern | Variable | Warning |
| Immune Support | TBD | Very Low | TBD | Real Concern | Variable | Warning |
| Protein Synthesis and Growth Hormone | TBD | Very Low | TBD | Real Concern | Variable | Warning |
What Sellers Say vs. What Studies Show
| “Boosts nitric oxide.” | Pills raise blood arginine, a lab marker. In one trial, blood vessels did not widen more. 7 |
| “Clinically proven.” | Only arginine for erectile function has a solid trial, and certainty is still low. Most products hold less than the 5 g studied. 8 |
| “Builds strength and endurance.” | Across 30 trials the gain was tiny, and it vanished when one 2010 trial was dropped. 9 |
| “Speeds recovery.” | We found no recent trial showing faster recovery or less soreness. |
| “Citrulline beats arginine.” | Citrulline raises blood arginine more, but no trial compares the two on real health results. |
| “It’s natural, so it’s safe.” | After a heart attack, 6 people taking arginine died versus none on placebo. 10 |
Trial ParametersIf you try it
| Who | Adults who have not had a heart attack, are not pregnant and take no nitrate, sildenafil-type or blood-pressure drug. No marketed benefit is established. |
| Dose | Erectile function trials used 5 to 6 g of arginine a day for 2 to 3 months. Exercise trials dosed 60 minutes before training. |
| Ceiling | No upper limit is set. NIH reports few safety concerns for arginine up to 9 g a day for days to weeks. 11 |
| Duration | Erectile function trials ran 2 to 3 months. Stop if nothing changes within a few weeks. |
| Form | Single-ingredient L-citrulline, citrulline malate or L-arginine. Typical retail products are likely underdosed. People with milk allergy should note the recalled citrulline powders. 8 |
| Ask First | After a heart attack, in pregnancy or breastfeeding, or with asthma; heart, erectile dysfunction, blood-thinning, diabetes or diuretic drugs. Not a substitute for treatment. |
How to Take It
| Pick a plan | Erectile function trials used 5 to 6 g of arginine a day for 2 to 3 months. No trial or agency sets one best dose. 1 |
| Time of day | For workouts, trials dosed about 60 minutes before training. 9 |
| With food | Not reported. |
| What to expect | Blood pressure may drop about 4 points. Erectile function gains took 2 to 3 months. Stop if nothing changes in a few weeks. 13 1 |
| How to take | Dissolve powder in water. Pick a label that states grams of citrulline or arginine per serving, not a blend weight. |
Works With / Don’t Mix With
✓ Works with
Erectile dysfunction medicine, only with your doctor. In one review, arginine plus tadalafil ranked above tadalafil alone. Only your prescriber can weigh the drug risks. 14
Nitrate-rich foods. USADA suggests beets, arugula and carrots first. We did not review their effect. 6
⚠ Ask first / don’t mix
A past heart attack. Do not take arginine. In one trial, 6 people on arginine died versus none on placebo. 10
Nitrates or sildenafil-type drugs. Together they may drop blood pressure too low. 12
Blood-pressure drugs. Blood pressure may fall too far. 12
Blood thinners. Bleeding risk may rise. 12
Diabetes drugs or potassium-sparing water pills. Doses may need to change, and potassium may climb. 12
Asthma or allergies. Arginine can make them worse. 12
Manufacturer Recalls & WarningsLast 36 months, newest first
| Date | Maker / Brand | Product | Action | Src |
|---|---|---|---|---|
| Mar 2025 | Cutler Nutrition | Amplify Peach Mango powder (NPN 80108126; L-citrulline 3,000 mg; lot 41252) | Health Canada recall RA-77186, Type II, for possible contact with milk-derived proteins during manufacturing. An allergen recall, not an ingredient finding. | 2 |
| 2025 | Believe Supplements | Brain Fuel (NPN 80106092; L-citrulline 825 mg), Performance EAA (NPN 80097651; 1,650 mg), Pre Fuel (NPN 80135145; 3 g) | Health Canada recall RA-77188 for contamination with milk-derived proteins. The page text we read does not show the date. | 3 |
Where to Buy
We compare products side-by-side not just on price, but on whether NSF lists the product as NSF/ANSI 173 Contents Certified (an independent lab confirms the label matches the contents), whether it is NSF Certified for Sport, whether USP lists it as USP Verified, and whether the seller says it is manufactured in the USA. We leave out a brand’s products for this supplement when, in the last 36 months, the FDA took action against that brand over this supplement (a Class I or II recall, a warning letter, an import alert or an advisory letter). We also leave out any brand with an FDA Class II recall or warning letter on any product. We also leave out any product named in a California Prop 65 notice or a non-US recall, along with that brand’s products of the same ingredient and form. Brands with other actions stay listed and are marked in the Recall Screen column. Our goal remains to provide you, the Consumer, with the information and data necessary to make an informed purchasing decision. Prices reflected below are static and subject to change.
Ratings above describe the ingredient’s research, not any product listed below.
| # | Retailer | Product | Price | NSF 173 | NSF Sport | USP | Mfg. in USA (per seller) | Recall Screen | Affiliate link |
|---|---|---|---|---|---|---|---|---|---|
| 1 | iHerb | Thorne, L-Arginine, 120 Capsules (500 mg per Capsule) | $44.00 | ✓ | ✓ | ✓* | View on iHerb ↗ | ||
| 2 | iHerb | EVLution Nutrition, L-Arginine, 1 g, 90 Tablets | $4.12 | ✓ | ✓ | View on iHerb ↗ | |||
| 3 | iHerb | fitcode, L-Arginine, 100 Capsules (750 mg per Capsule) | $6.30 | ✓ | ✓ | View on iHerb ↗ | |||
| 4 | iHerb | EVLution Nutrition, L-Citrulline2000®, 90 Veggie Capsules (666 mg per Capsule) | $10.13 | ✓ | ✓ | View on iHerb ↗ | |||
| 5 | iHerb | NOW Foods, Sports, L-Arginine, 1,000 mg, 60 Tablets | $11.03 | ✓ | ✓* | View on iHerb ↗ | |||
| 6 | HerbsPro | Source Naturals, L-Citrulline, 500 mg, 60 Caps | $11.73 | ✓ | ✓ | View on HerbsPro ↗ | |||
| 7 | HerbsPro | Now Foods, L-Citrulline, 750 Mg, 90 Veg Caps | $15.62 | ✓ | ✓* | View on HerbsPro ↗ | |||
| 8 | Green's Nutrition | Nutricost L-Citrulline Capsules 120 Count | $15.95 | ✓ | ✓* | View on Green's Nutrition ↗ | |||
| 9 | Green's Nutrition | Solaray L-Arginine 100 Caps | $20.89 | ✓ | ✓* | View on Green's Nutrition ↗ | |||
| 10 | Green's Nutrition | Pure Encapsulations L-Arginine 180 Caps | $49.50 | ✓ | ✓* | View on Green's Nutrition ↗ |
Sources
1. Menafra D et al. Long-term oral L-arginine 6 g a day and vasculogenic erectile dysfunction: multicentre randomized trial. Journal of Endocrinological Investigation, 2022. doi.org/10.1007/s40618-021-01704-3
2. Recall RA-77186: Amplify Peach Mango powder (Cutler Nutrition). Health Canada Recalls and Safety Alerts, Last updated 26 Mar 2025. recalls-rappels.canada.ca/en
3. Recall RA-77188: Believe Supplements Brain Fuel, Performance EAA and Pre Fuel powders. Health Canada Recalls and Safety Alerts, 2025. recalls-rappels.canada.ca/en
4. Warning letter to Valentine Enterprises, Inc., MARCS-CMS 705119. US Food and Drug Administration, 17 Jul 2025. www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/valentine-enterprises-inc-705119-07172025
5. L-arginine functional ingredient recognition 2015-19 (Korean original read in translation). Ministry of Food and Drug Safety, Korea (Food Safety Korea portal), 18 Jun 2015. www.foodsafetykorea.go.kr/
6. Do athletes really need nitric oxide supplements to boost performance?. U.S. Anti-Doping Agency, 1 Apr 2022; modified 2 Mar 2026. www.usada.org/spirit-of-sport/nitric-oxide-supplements/
7. Grannes et al. Citrulline malate 6 g and 12 g and flow-mediated dilation in healthy men: crossover trial. Frontiers in Physiology, 2026. doi.org/10.3389/fphys.2026.1773582
8. Petre et al. Nutraceuticals for erectile dysfunction: systematic review and meta-analysis, with a survey of marketed products. Nutrients, 2023. doi.org/10.3390/nu15173677
9. Wang et al. Citrulline malate and exercise performance: three-level meta-analysis of 30 randomized trials. Nutrients, 2026. doi.org/10.3390/nu18121881
10. Schulman SP et al. L-arginine therapy in acute myocardial infarction: the VINTAGE MI randomized trial. JAMA, 2006. doi.org/10.1001/jama.295.1.58
11. Exercise and Athletic Performance: Health Professional Fact Sheet. NIH Office of Dietary Supplements, Read 7 Oct 2026. ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformance-HealthProfessional/
12. L-arginine: safety, side effects and interactions. Mayo Clinic, 16 Mar 2026. www.mayoclinic.org/drugs-supplements-l-arginine/art-20364681
13. Luo et al. Citrulline and watermelon supplementation and blood pressure: meta-analysis of 15 randomized trials. Clinical Nutrition ESPEN, 2025. doi.org/10.1016/j.clnesp.2025.07.1130
14. Barbonetti A et al. Nutraceuticals and PDE5 inhibitors for erectile dysfunction: network meta-analysis of 15 randomized trials. Journal of Sexual Medicine, 2024. doi.org/10.1093/jsxmed/qdae123
15. Winer N et al. L-citrulline in pre-eclampsia (CITRUPE): double-blind randomized trial. American Journal of Clinical Nutrition, 2025. doi.org/10.1016/j.ajcnut.2024.12.001
16. openFDA food enforcement records, search for citrulline, report dates 2024 to 7 Oct 2026 (no matches). US Food and Drug Administration (openFDA), 7 Oct 2026. api.fda.gov/food/enforcement.json?search=product_description:citrulline
17. openFDA drug enforcement records D-0055-2026 and D-0056-2026 (GenoGenix LLC) and D-0477-2025 (Thrive Health Solutions). US Food and Drug Administration (openFDA), 2025 and 2026. api.fda.gov/drug/enforcement.json?search=recall_number:%22D-0055-2026%22
18. L-Citrulline Supplements Review; product results behind a paywall. ConsumerLab.com, 25 Jun 2026. www.consumerlab.com/
19. Shi et al. Oral L-arginine and 24-hour ambulatory blood pressure: meta-analysis. Nitric Oxide, 2026. doi.org/10.1016/j.niox.2026.07.004
