CircO2 Review: Nitric Oxide Supplement for Blood Flow, Energy & Circulation?

Search interest around nitric oxide supplements has grown because nitric oxide sits at the intersection of exercise performance, vascular biology and everyday circulation. It is a short-lived signalling molecule involved in the regulation of blood-vessel tone, and researchers have spent decades studying how nitric oxide is produced, preserved and influenced by diet. That makes products marketed as nitric oxide boosters an interesting category—but it also makes them easy to oversell.

One product attracting attention is CircO2, sold by Advanced Bionutritionals. The manufacturer's current presentation positions CircO2 as a fast-dissolving nitric oxide and circulation support lozenge. The formula is described as containing beet root powder, hawthorn berry extract, L-citrulline, sodium nitrite, vitamin C, vitamin B12 and magnesium. In this review, we separate what the company says from what independent research can actually tell us.

What Is CircO2?

CircO2 is marketed as a dietary supplement designed to support nitric oxide production and circulation. Unlike a conventional capsule, the product is presented as a quick-dissolve tablet intended to dissolve in the mouth. The manufacturer says this delivery approach is important because oral bacteria participate in the nitrate-to-nitrite step of the body's enterosalivary nitrate pathway. Independent research does support the underlying biological pathway: oral nitrate-reducing bacteria can convert dietary nitrate to nitrite, which can subsequently contribute to nitric oxide availability. citeturn3search0turn3search1

That mechanism is scientifically interesting, but it should not be confused with proof that every product using a lozenge format will produce a specific clinical outcome. The research on nitric oxide biology is broader than the evidence for any individual commercial formulation. Readers considering CircO2 should therefore look at both the formula and the quality of evidence supporting the product's specific claims.

Why Nitric Oxide Matters to Blood Flow

Nitric oxide helps regulate vascular tone. In simple terms, signalling through nitric oxide can contribute to relaxation of vascular smooth muscle, which affects blood flow. Nitric oxide is produced through the well-known L-arginine/nitric oxide synthase pathway, but dietary nitrate can also enter a second route in which nitrate is reduced to nitrite and then, under suitable conditions, to nitric oxide. Reviews of the literature describe the mouth as an important part of this nitrate-nitrite-nitric oxide pathway. citeturn3search6turn3search8

This is one reason beetroot and leafy green vegetables are frequently discussed in performance nutrition. The important nuance is that biological plausibility is not the same as guaranteed performance improvement. Human trials and meta-analyses have produced mixed results depending on the dose, exercise type, population and outcome measured.

What Is Actually Inside the Formula?

According to the manufacturer's current supplement-facts presentation, one serving is one tablet and the formula provides vitamin C, vitamin B12 and magnesium alongside a proprietary nitric-oxide blend. The listed blend contains beet root powder (Beta vulgaris), hawthorn berry extract (Crataegus laevigata), L-citrulline and sodium nitrite. The label shown on the product page lists 100 mg of vitamin C, 1,000 mcg of vitamin B12 and 4 mg of magnesium per serving, with 420 mg for the proprietary blend. These are manufacturer-listed specifications and should be checked against the live label before purchase.

For someone comparing nitric oxide supplements, this ingredient combination is notable because it approaches the pathway from more than one direction. Beetroot supplies nitrate-related compounds; L-citrulline is a precursor that can raise arginine availability; and the oral-delivery format is intended to interact with the nitrate-reduction process in the mouth. Vitamin C and B12 are included as additional nutrients, while hawthorn is commonly associated with cardiovascular and circulatory research.

If you want to inspect the manufacturer's current ingredient presentation directly, view the CircO2 product page here before making any decision.

Beetroot and Nitrate: What Does the Research Say?

Beetroot is one of the better-studied dietary sources of nitrate. Research reviews describe nitrate as a substrate that can contribute to nitric oxide formation through the enterosalivary pathway. A 2024 systematic review and meta-analysis of beetroot juice in adults with hypertension found a reduction in clinical systolic blood pressure, although the certainty of evidence was rated low and results varied between studies. That research involved beetroot juice interventions, not CircO2, so it should not be presented as proof that CircO2 produces the same effect. citeturn3search10

Exercise research is similarly nuanced. A 2022 systematic review and meta-analysis found no significant overall improvement in aerobic performance from citrulline supplementation, while a 2026 meta-analysis of citrulline malate reported a small overall performance effect but rated the certainty of evidence low to very low and described the benefits as context-dependent. citeturn0search0turn0search2

That distinction matters when reading viral supplement headlines. A promising ingredient can have a credible mechanism and still deliver a modest, inconsistent or population-specific outcome. A sensible CircO2 review therefore needs to keep ingredient research and product-specific evidence in separate boxes.

The Oral Microbiome Angle

The most distinctive part of CircO2's marketing is its emphasis on the mouth. Independent research does support the idea that specific oral bacteria participate in nitrate reduction. A systematic literature review describes the nitrate-nitrite-nitric oxide pathway as involving the oral microbiome, while newer reviews continue to investigate how oral bacterial communities influence nitric oxide bioavailability. citeturn3search0turn3search2

This helps explain why the manufacturer chose a dissolving lozenge rather than simply presenting CircO2 as an ordinary swallowed tablet. However, readers should be careful with claims about mouthwash, toothpaste or oral bacteria. A systematic review found that antibacterial mouthwash can influence the nitrate-nitrite pathway and circulating nitrate/nitrite measures, but that does not mean people should abandon evidence-based oral hygiene. citeturn3search7

The practical takeaway is straightforward: the oral microbiome is a legitimate area of nitric oxide research, but it is not a reason to replace dental care with a supplement.

What About the “200% in 20 Minutes” Claim?

The manufacturer's sales page prominently promotes a claim that nitric oxide levels increased by 200% within 20 minutes in testing of the CircO2 lozenge. It also describes a 34% increase in blood flow in a separate test. These figures are manufacturer-reported product claims, not conclusions that should automatically be generalized to every user.

That distinction is especially important because the exact study design, participant characteristics, measurement method and clinical significance determine how a percentage should be interpreted. A rise in a biomarker does not automatically mean a person will experience a corresponding improvement in stamina, memory, blood pressure or sexual function. Independent research can support the underlying physiology without validating every marketing endpoint.

For that reason, anyone researching the best nitric oxide supplement should treat large numerical promises as a reason to inspect the evidence, not as a guarantee of a particular result. You can review the manufacturer's supporting information and current offer by visiting the CircO2 page.

Could CircO2 Fit an Exercise-Focused Routine?

For fitness readers, the most realistic way to think about a nitric oxide supplement is as an optional addition to an already solid training and nutrition routine. Aerobic conditioning, progressive resistance training, adequate sleep, sufficient dietary protein, hydration and a nutrient-dense diet have a much larger role in long-term fitness than any single supplement.

Someone interested in circulation support may also choose nitrate-rich foods such as leafy greens and beetroot. For athletes, the research on nitrate and citrulline is worth considering, but outcomes vary. The 2019 systematic review of acute citrulline supplementation for strength and power found mixed results across studies, illustrating why supplement marketing should not be treated as a substitute for performance evidence. citeturn0search1

If a reader decides to investigate CircO2, the practical approach is to follow the current label and manufacturer directions, avoid stacking multiple products with overlapping ingredients without checking the totals, and track meaningful outcomes rather than relying solely on sensations such as a temporary “pump.”

Who Should Be More Cautious?

Because nitric oxide pathways can influence vascular tone and blood pressure, supplement decisions deserve extra care for people who take medicines that affect blood pressure or circulation, have cardiovascular conditions, have been advised to restrict certain supplements, or are pregnant or breastfeeding. The manufacturer's own page advises people with low blood pressure to consult a physician before using CircO2.

Do not use a supplement review as a substitute for medical assessment. In particular, someone considering a product because of high blood pressure, chest symptoms, unexplained fatigue, erectile difficulties, numbness, dizziness or changes in exercise tolerance should discuss those symptoms with a qualified healthcare professional rather than attempting to self-treat them with a supplement.

CircO2 vs. Ordinary Nitric Oxide Supplements

What makes CircO2 interesting from a product-comparison perspective is its delivery format and combination of ingredients. Many nitric oxide products focus primarily on L-citrulline, L-arginine, beetroot or a pre-workout blend. CircO2 instead emphasizes a quick-dissolve lozenge and a combination that includes nitrate-related ingredients, L-citrulline and micronutrients.

That does not automatically make it superior. The right comparison depends on the question being asked: Are you looking for a pre-workout ingredient? A dietary nitrate source? A circulation-focused supplement? A convenient lozenge? Or simply a product with a particular ingredient profile? Comparing the actual label, serving size, ingredient amounts, evidence and price is more informative than relying on a “best” label.

Final Verdict: Interesting Formula, But Read Beyond the Headline

CircO2 sits in a scientifically interesting category. Nitric oxide is a genuine physiological signalling molecule, the nitrate-nitrite pathway is well documented, and oral bacteria have a meaningful role in nitrate metabolism. Beetroot and citrulline also have a substantial research history. Those facts explain why nitric oxide supplements continue to attract attention in both fitness and healthy-aging circles.

At the same time, the evidence does not justify turning every nitric oxide claim into a promise. Research on citrulline and exercise performance is mixed; beetroot research is context-dependent; and product-specific claims require product-specific evidence. CircO2's manufacturer reports rapid changes in nitric oxide and blood flow, but those claims should be understood as claims from the seller rather than universal outcomes.

For shoppers, the strongest approach is to look at the current label, understand what the product is designed to do, compare the evidence behind individual ingredients, and consider whether the supplement fits your goals and circumstances. If you want to see the current product information for yourself, visit the official CircO2 offer page.

Sources & Evidence Notes