Best Nitric Oxide Supplement? What L-Arginine, L-Citrulline and Beet Root Can and Can't Do (2026)

There is no proven best nitric oxide supplement, and none is approved to treat erectile dysfunction. The NIH Office of Dietary Supplements finds little support for arginine or citrulline as performance aids, while beet juice improved endurance in many, but not all, studies. Mayo Clinic says high doses of L-arginine show some promise for ED, but its L-arginine guidance warns that combining it with nitrates, sildenafil or blood pressure drugs might drop blood pressure too low.

Below: the research on each common ingredient, the drug interactions that make this category riskier than most, label checks, and the official facts on Nitric Boost Ultra, the nitric oxide product we have reviewed. We haven't tested these products, and we don't rank them.

What nitric oxide does, and what the supplements contain

Nitric oxide expands blood vessels and increases blood flow. Supplements don't contain it; they supply raw materials the body can turn into it. As the Office of Dietary Supplements (ODS) explains, the body converts arginine into nitric oxide, the kidneys turn most citrulline into arginine, and beets are rich in nitrate, some of which the body also converts to nitric oxide.

That's why the same ingredients are sold for workouts, circulation and male sexual performance, even though the evidence differs for each goal.

If erectile dysfunction is the reason you're shopping, start with a doctor rather than a powder. MedlinePlus notes that ED becomes more common with age but isn't a natural part of aging, and that it can be a sign of clogged blood vessels or nerve damage from diabetes. NIDDK lists lifestyle changes, counseling and prescription medicines such as PDE5 inhibitors among the treatments, and asks men to talk with a health care professional before using supplements or ordering ED medicine online.

What the research says, ingredient by ingredient

L-arginine

ODS says the research is limited, but arginine supplements seem to have little to no effect on strength training or on aerobic exercise such as running and cycling; studies used 2 to 20 grams a day. Up to 9 grams a day for several weeks seems safe, while more can cause stomach discomfort and slightly lower blood pressure.

For ED, Mayo Clinic reports that some research shows high doses help by letting blood vessels open wider. Possible side effects include stomach pain, bloating, headache, insomnia and diarrhea, and Mayo says not to take L-arginine with sildenafil. Its L-arginine page adds that the supplement isn't recommended after a recent heart attack and can worsen allergies or asthma.

L-citrulline

ODS calls the evidence for citrulline as a performance supplement limited: a few studies suggest it might help, hinder or have no effect, and there isn't enough research to know whether it's safe. A Cleveland Clinic dietitian describes the case for ED as unsettled, lists bloating, cramping, diarrhea and sweating as possible side effects, and advises seeing a provider first because supplements can interact with other medicines. She also prefers plain L-citrulline over citrulline malate, the form bound to malic acid, because research on the malate form is thinner and conflicting.

Beet root and dietary nitrate

Beets are among the best food sources of nitrate. According to ODS, many but not all studies found beet juice improved performance in aerobic activities such as running, cycling and rowing, more reliably in recreational exercisers than in highly trained athletes. Studies typically used about 2 cups of juice 2.5 to 3 hours before exercise, and whether beetroot powder supplements have the same effect isn't known. Moderate amounts are safe, though urine can turn pink or red. Cleveland Clinic notes that beetroot powder is high in oxalates, which can raise the risk of kidney stones, especially if you've had them before, and calls claims about beetroot and sexual health thin on scientific confirmation.

Herbs and vitamins added to performance blends

Multi-ingredient powders often pair the precursors with herbs, and Mayo Clinic's review of ED supplements is blunt about several:

• Ginkgo may boost blood flow, but there isn't enough proof that it helps ED, and it may rarely raise the risk of bleeding and irregular heartbeats. NCCIH adds that it may increase bleeding in people taking anticoagulants such as warfarin, and that there's no conclusive evidence it helps any health condition.
• Horny goat weed (epimedium) lacks enough evidence for ED. Side effects can include dizziness, dry mouth, nosebleed, thirst and vomiting, and it may affect heart or breathing functions.
• Yohimbe has been linked with dangerous side effects, including higher blood pressure, a fast or irregular heartbeat, heart attack and seizures. Mayo says not to use it without a health care professional's guidance.
• Niacin (vitamin B3) is a vitamin, not an herb, but it appears in some blends. The ODS niacin fact sheet says supplements with 30 mg or more of nicotinic acid can make the skin on the face, arms and chest turn red and burn, tingle and itch, and sets the adult upper limit from supplements at 35 mg a day.

One caveat covers every blend: ODS points out that most ingredient combinations in performance supplements haven't been studied, so nobody knows how well or how safely they work together.

Nitrates, ED medicines and blood pressure

This is where nitric oxide boosters differ from most supplements. Mayo Clinic's L-arginine page warns that taking it with nitrates for chest pain, with sildenafil, or with blood pressure drugs might make blood pressure fall too low. It also flags blood thinners (bleeding risk), diabetes drugs (blood sugar may drop) and potassium-sparing diuretics such as spironolactone (risk of high potassium).

Prescription ED medicines carry a related rule. Mayo's page on Viagra and other oral ED medicines says they might not work or might be dangerous for men who take nitrate medicines, which are often prescribed for chest pain, and MedlinePlus tells anyone prescribed sildenafil to let their doctor know about nitrates such as nitroglycerin.

That matters for supplements because some aren't what they claim. Mayo Clinic warns that some products sold as "herbal Viagra" contain ingredients like those in prescription medicines, and some contain the real drug. The FDA says many products sold for sexual enhancement, including male enhancement supplements and stamina pills, are likely to be contaminated with dangerous hidden ingredients. It adds that they are sometimes falsely sold as dietary supplements or all-natural treatments, often have many positive reviews or social media buzz, and are sold online and in stores.

How to read a nitric oxide supplement label

• Find the grams. The research ODS describes used grams, not milligrams: 2 to 20 g of arginine a day, up to 6 g of citrulline a day for as long as 16 days, and about 2 cups of beet juice. A label that lists these ingredients without amounts, or tucks them into a proprietary blend, leaves you nothing to compare. Under FDA labeling rules, a blend only has to show its total weight and list its ingredients by descending weight.
• Note the citrulline form. "L-citrulline DL-malate" is citrulline bound to malic acid, the malate form Cleveland Clinic's dietitian ranks behind plain L-citrulline.
• Check the niacin line. ODS ties flushing to 30 mg or more of nicotinic acid, so the amount and form both matter.
• Scan for yohimbe and banned stimulants. Mayo warns against unsupervised yohimbe, and ODS notes the FDA prohibits ingredients such as DMAA, ephedra and androstenedione.
• Look for testing you can verify. ODS names NSF's Certified for Sport program, Informed-Choice and the Banned Substances Control Group as services that screen products for banned substances. Certified products can carry the certifier's logo and are listed on its website.
• Read claims as marketing. Blood-flow and stamina wording is a structure/function claim, and the FDA has no authority to approve supplements before they're sold. Our explainer covers why supplements are not FDA-approved.

Red flags

• "Herbal Viagra" or "works like the prescription" pitches. Mayo Clinic says the FDA has banned many of these products and that some risky ED remedies are still on the market.
• Instant results, a "secret ingredient" or a "new discovery." These are on the FDA's list of health fraud tip-offs, which also warns that marketplace and social media reviews can be fake.
• No amounts on the label. If a seller won't say how much arginine or citrulline is in a scoop, you can't judge the product against the research.
• Look-alike listings. In September 2026 search results, an Amazon listing under the Nitric Boost Ultra name came from a different company, and a Walmart category page for the name showed 22 separate listings. Buy through the official site named in our review.

Nitric Boost Ultra: what the official pages say

Nitric Boost Ultra is the nitric oxide product we have reviewed. The official sales copy calls it simply Nitric Boost; "Ultra" appears in one official page title and in the name of our review. These facts come from its official pages, checked on September 30, 2026.

The seller markets it for male sexual performance and erection support through nitric oxide, and its page cites ED research. The formula includes all three precursors discussed above, but without amounts there's no way to tell whether a scoop comes anywhere near the grams used in studies. Two of its herbs, ginkgo and horny goat weed, are ones Mayo Clinic says lack enough evidence for ED, and ginkgo and L-arginine both carry the interaction warnings above. The sources in this guide don't evaluate dong quai or D-aspartic acid, so we make no claims about them. The seller says the powder is made in the USA from domestic and foreign ingredients in a GMP-certified facility, and describes it as non-GMO and vegan. If you do order, our guide to ClickBank and Digistore24 refunds explains how refunds through these platforms work.

For the full breakdown, including where to buy the authentic product, read our Nitric Boost Ultra review.

One more label on our site lists nitric oxide precursors. Flush Factor Plus, a once-daily capsule its seller markets for healthy legs, leg and ankle fluid balance, and mobility, includes L-citrulline DL-malate and beet root extract inside a 500 mg proprietary blend, so the amount of each isn't disclosed. It isn't sold as a nitric oxide or male performance product.

Talk to a doctor first if any of these apply

• You take a nitrate for chest pain, such as nitroglycerin, or an ED medicine such as sildenafil (Mayo Clinic).
• You take blood pressure medicine, a blood thinner, diabetes medicine or a potassium-sparing diuretic.
• You've had a recent heart attack, or you have asthma or allergies.
• You've had kidney stones and the product contains beetroot.
• You have heart disease or diabetes; Mayo Clinic says talking with your provider before trying any ED supplement is especially important then.
• You have ED at all. MedlinePlus notes it can be a sign of health problems that go untreated if you don't see your doctor.

For other products in this area, browse our men's health reviews.