Nitric Oxide Supplements in 2026: Beetroot, L-Citrulline and Hawthorn Explained, Plus an Honest Look at CircO2

Somewhere between a gym YouTube video and a late-night health article, most of us have met the idea of nitric oxide: a molecule that relaxes your blood vessels, helps blood flow and, according to a lot of supplement marketing, is the secret behind everything from stamina to a healthier heart. It is a tidy story. It is also one where the science is real, the supplement claims are often inflated, and the safety questions matter more than usual.

This guide is our attempt to sort the real from the hype. We will explain what nitric oxide does, how beetroot, L-citrulline and hawthorn are meant to raise it, what trials have actually shown, and why anyone on blood pressure or heart medicine should pause before buying anything in this category. Near the end we will look at one product, CircO2, and give you its strengths and weak spots side by side. If you only want the product facts, our full CircO2 review has them in one place.

Key takeaways (the 60-second version)

• Nitric oxide is real and important. It helps blood vessels relax and widen, which is part of how your body regulates blood flow.
• Beetroot has the best evidence. A meta-analysis found beetroot juice lowered systolic blood pressure by about 3.5 mm Hg on average versus control drinks, a modest effect with a lot of variation between studies.
• L-citrulline is small-study territory. A meta-analysis of eight small trials suggested it may reduce systolic blood pressure, and the diastolic effect appeared only at around 6 grams a day or more.
• Doses decide everything. A product that hides its main ingredients in a blend gives you no way to compare it with what the studies used.
• Medicine interactions are the big risk. Ingredients that relax blood vessels can add to the effect of blood pressure, heart and erectile dysfunction medicines.
• Mouthwash can undercut nitrate. Antibacterial mouthwash reduced blood nitrite after a nitrate dose in one small study.

What is in this guide

1. Key takeaways (the 60-second version)
2. What nitric oxide is, in plain English
3. How supplements try to raise it: nitrate, citrulline and herbs
4. What the research says (and does not say)
5. The mouthwash catch most people miss
6. Lifestyle first: what actually supports healthy blood pressure
7. CircO2, reviewed honestly
8. Safety, interactions and who should skip
9. A buyer's checklist
10. Frequently asked questions

1. What nitric oxide is, in plain English

Nitric oxide (NO) is a small gas molecule your body makes in the lining of your blood vessels. When it is released, the muscle in the vessel wall relaxes, the vessel widens and blood flows more easily. That is a big part of how your circulation adjusts to what you are doing, whether that is climbing stairs or sitting still.

It is also, importantly, short-lived. Your body makes it on demand and uses it within moments. You cannot swallow nitric oxide itself, so supplements try a different strategy: provide raw materials your body can turn into it. There are two main routes, and they are worth understanding because most products lean on one or both.

Route one: nitrate, then nitrite, then nitric oxide

Leafy greens and beetroot are rich in dietary nitrate. Bacteria in your mouth convert nitrate into nitrite, and your body can then turn nitrite into nitric oxide. It is a surprisingly roundabout journey, and it depends on your oral bacteria doing their job, which is why the mouthwash point later in this guide matters.

Route two: the amino acid pathway

Your body can make nitric oxide from L-arginine. L-citrulline, found in watermelon and sold as a supplement, is converted into L-arginine in the body, which is why it appears in so many nitric oxide formulas.

Where herbs like hawthorn fit in

Hawthorn berry is a traditional heart-health herb. It is often added to circulation products, although its evidence is a different kind from nitrate or citrulline, as we will see.

Curious about the product we review later? Check today's price on the official site

2. How supplements try to raise it: nitrate, citrulline and herbs

A quick comparison helps, because these ingredients do different things and carry different levels of proof.

The big point is that these are not interchangeable. A beetroot drink with measured nitrate, a gram of citrulline and a fraction of a hawthorn extract are three very different experiments. When a label bundles them together without telling you how much of each is inside, you cannot tell which experiment you are running.

3. What the research says (and does not say)

Here is where nitric oxide marketing tends to get ahead of itself, so let us stay close to the published work.

Beetroot: modest, real, but variable

The strongest signal in this category comes from beetroot. A systematic review and meta-analysis in Advances in Nutrition found that beetroot juice was associated with lower blood pressure than control drinks: roughly 3.5 mm Hg lower for systolic pressure and about 1.3 mm Hg lower for diastolic. The effects were larger in trials lasting 14 days or more. The authors also flagged the limits. The studies were very different from one another in people, doses and duration, the inclusion rules were broad, and they called for larger, longer trials in people who actually have hypertension.

A few points of context help. A drop of a few points is genuine, but it is small compared with what blood pressure medicine or sustained lifestyle change can do. And these were studies of beetroot juice, a food-based product, not of tablets with undisclosed amounts. Nothing here shows that a particular tablet works.

L-citrulline: promising, but small trials

A systematic review and meta-analysis of L-citrulline and blood pressure pooled eight small trials, each with 12 to 34 participants. The authors concluded that citrulline may reduce systolic blood pressure, and that the diastolic reduction was significant only at doses of 6 grams a day or more. That last detail is the one to remember. Six grams is 6,000 mg, so a product with a few hundred milligrams of citrulline in a shared blend is nowhere near the amounts that produced the clearest results.

Hawthorn: conflicting and cautionary

Hawthorn has a long traditional history, but the modern evidence is less tidy. The NIH's National Center for Complementary and Integrative Health says there is conflicting evidence on hawthorn for heart failure, and not enough evidence for other heart conditions. It lists possible side effects including dizziness, nausea, vomiting, diarrhea and muscle pain, notes that no studies have tested use beyond 16 weeks, and says safety in pregnancy and breastfeeding is poorly known. It also repeats the sensible advice to talk to a health care provider before using any herbal product if you take medicine.

Why testimonials mislead here

People who feel more energy after starting a supplement are often also sleeping better, moving more or simply paying more attention to their health. Blood pressure itself rarely produces symptoms, so nobody can "feel" it change. A cautious reader treats reviews as color, not proof, and checks blood pressure with a real cuff.

4. The mouthwash catch most people miss

Remember the nitrate route from earlier, where bacteria in your mouth turn nitrate into nitrite. That step is easy to disrupt. A small study in 10 healthy men, reported in Medicine & Science in Sports & Exercise, found that antibacterial mouthwash lowered plasma nitrite compared with the other study arms, both with and without beetroot juice, while plasma nitrate was not reduced. The mouthwash did not change blood pressure or salivary cortisol in that short-term setting.

This was a small meeting abstract, so we would not build a rulebook on it. But it illustrates a real mechanism: if you depend on nitrate to make nitrite, the bacteria that do the conversion matter. If you use antibacterial mouthwash regularly and are counting on a nitrate-based product, ask your dentist or doctor before changing your routine.

5. Lifestyle first: what actually supports healthy blood pressure

If circulation or blood pressure is the reason you are here, start with the habits that have the strongest evidence. A randomized trial called TRIUMPH, highlighted in an American Heart Association news release, followed 140 adults with resistant high blood pressure for four months. Those who joined a supervised program of weekly dietary counseling and exercise training three times a week saw office systolic pressure fall about 12 points, versus about 7 points for people given written guidance to follow alone. On 24-hour monitoring, the supervised group dropped about 7 points while the self-guided group showed no change. It came from a single institution and depends on people sticking with the changes, but it shows how powerful structured habits can be.

1. Move regularly. Walking, cycling or swimming most days, plus some strength work, is the single most reliable habit for circulation.
2. Eat the DASH way. Plenty of vegetables, fruit, whole grains and legumes, less salt and fewer ultra-processed foods. Leafy greens and beets already supply nitrate. If you want easy ways to add produce, our smoothie diet resource is a simple start.
3. Keep a healthy weight and limit alcohol.
4. Do not smoke. Few things damage blood vessels faster.
5. Sleep well and manage stress. Both show up in your blood pressure readings.
6. Measure and see your doctor. A home blood pressure cuff and a regular check-up beat any guess. Never stop or change prescribed medicine because of a supplement.

If low energy is your main worry rather than circulation, see our guide to mitochondrial support supplements. For muscle and recovery, read our essential amino acid guide, and for memory and focus, our memory supplements guide.

6. CircO2, reviewed honestly

CircO2 is a daily dietary supplement from Advanced Bionutritionals, a US supplement company based in Norcross, Georgia. It is sold as quick-dissolve tablets (the sales page calls them lozenges) and marketed for circulation, energy and healthy aging. It is endorsed by naturopathic physician Dr. Greg Eckel, who is paid by the company. The details below come from the manufacturer's label and sales page, as summarized on our full CircO2 review.

What is on the label

The serving is one tablet, and each box holds 30 tablets, a 30-day supply. The tablet is placed on the tongue to dissolve.

What it costs

Check today's price on the official CircO2 site

What reviewers say

On the manufacturer's site CircO2 averages 3.9 out of 5 from 1,618 reviews, and 74% of reviewers say they would recommend it. Several customers mention more energy or stamina. These are reviews on the seller's own page, not independent trials, and individual results vary. Compared with the other products we review, this is the lowest recommendation rate, which is worth noticing.

Strengths

• A quick-dissolve tablet, one a day, with 30 servings per box.
• Combines beet root, L-citrulline and hawthorn with vitamins B12 and C.*
• Vitamin amounts and the total weight of the blend are shown on the label.
• A 90-day guarantee that covers an empty box, and free shipping on 3- and 6-box orders.

Weak spots

• The main ingredients (beet root, hawthorn, L-citrulline and sodium nitrite) share a 420 mg proprietary blend, so the dose of each is not disclosed.
• Studies of L-citrulline tend to use grams a day, far more than can fit in a 420 mg blend shared with three other ingredients.
• It contains sodium nitrite, an unusual supplement ingredient, and the amount is not shown.
• Vitamin B12 is 1,000 mcg, far above what most adults need.
• The sales page claims, such as a 200% rise in nitric oxide in 20 minutes or lower blood pressure, are not backed by evidence we could verify for this product, and we found no published trial of CircO2 itself.
• The endorsing doctor is paid by the company. That is common, but you deserve to know.
• The tablets contain xylitol, which is toxic to dogs.

Who it may suit

• Adults curious about a circulation-focused supplement who have checked with their doctor first.*
• People who prefer a quick-dissolve tablet to capsules.
• Anyone comfortable with a proprietary blend who does not take blood pressure or heart medicine.

Who should skip it, or ask first

• Anyone taking blood pressure, heart or erectile dysfunction medicine, including digoxin.
• Anyone with low blood pressure, a heart condition or a blood condition.
• Anyone who is pregnant or nursing.
• Anyone who wants every ingredient dose disclosed.
• Households with pets that might eat the tablets.

7. Safety, interactions and who should skip

Of everything we review, nitric oxide products deserve the most careful read of the safety section, because they are meant to affect your blood vessels. Use this as a conversation starter with your doctor or pharmacist.

Remember what the NIH says about hawthorn: some side effects include dizziness, nausea and diarrhea, and a specific preparation in one study was linked to early heart failure progression, with the cause unclear. Combine that with the NIH's general advice in its guide to using dietary supplements wisely: tell every provider about every supplement, do not assume a label matches the contents, and stop and call your provider if you have side effects.

8. A buyer's checklist for any nitric oxide supplement

1. Are individual doses shown? A proprietary blend hides what you are actually getting.
2. Do doses resemble the studies? Compare citrulline and nitrate amounts with the research, not just the ingredient names.
3. Is there nitrite, and how much? It is an unusual ingredient, and the amount should be disclosed.
4. Are the claims believable? Precise percentage jumps in minutes are red flags.
5. Is it cheaper as food? Beets, leafy greens and watermelon supply nitrate and citrulline for pennies.
6. Is the guarantee real? Check who pays return shipping.
7. Did you ask your doctor? Especially with any medicine for blood pressure or the heart.

The FDA's FDA 101: Dietary Supplements guide explains how supplements are regulated. In short, they are not approved for effectiveness before they are sold, so your own label-reading matters.

Want more to compare? Browse all of our supplement reviews, see how we earn money on our affiliate disclosure page, or read more guides on the Bionwise blog. You may also like our reviews of Advanced Mitochondrial Formula, Advanced Amino Formula and Advanced Memory Formula, and our guide to GLP-1 hair and nail supplements.

Final verdict

Nitric oxide is genuinely important, and beetroot has real, modest evidence behind it. L-citrulline looks interesting at doses far higher than most tablets contain, and hawthorn is a mixed bag with some safety questions. The most reliable ways to support circulation are still regular movement, a vegetable-rich diet, not smoking, good sleep and a relationship with your doctor.

If you want to try a supplement anyway, choose one with disclosed doses, believable claims and a real guarantee, and speak to your doctor first. CircO2 is convenient and comes with a guarantee, but its undisclosed blend, its sodium nitrite and its unverified headline claims make it a product to approach carefully, and not at all if you take blood pressure or heart medicine.

See current pricing and the 90-day guarantee on the official site

Disclosure: this post contains an affiliate link. We may earn a commission at no extra cost to you if you buy through it. Our opinions are our own; see our affiliate disclosure.

9. Frequently asked questions

Sources and further reading

1. The Nitrate-Independent Blood Pressure-Lowering Effect of Beetroot Juice: A Systematic Review and Meta-Analysis. Advances in Nutrition, 2017. Read source
2. Effects of L-citrulline supplementation on blood pressure: A systematic review and meta-analysis. Read source
3. NIH National Center for Complementary and Integrative Health. Hawthorn. Read source
4. Anti-bacterial mouthwash reduces plasma nitrite following dietary nitrate supplementation but does not alter stress response. Medicine & Science in Sports & Exercise, 2017 (abstract). Read source
5. American Heart Association. Healthy changes in diet, activity improved treatment-resistant high blood pressure. Read source
6. NIH National Center for Complementary and Integrative Health. Using Dietary Supplements Wisely. Read source
7. U.S. Food and Drug Administration. FDA 101: Dietary Supplements. Read source

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. Medical disclaimer: this article is for general educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting any supplement, particularly if you take prescription medicines, are pregnant or breastfeeding, or have a medical condition. Never stop or change prescribed medicine because of a supplement. Individual results vary.