CircO2 Review: What the Research Actually Says

The Quick Summary & Label Transparency Check

Medical & FDA Disclaimer

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.

This review is for informational purposes only and is not medical advice. This is an unusually important section to actually read for this specific product. Nitric-oxide-boosting ingredients (L-citrulline and dietary nitrates from beetroot, both present in this formula) have a well-documented interaction with certain prescription medications, detailed in full below. Please read that section, and talk to your doctor or pharmacist, before starting this product if you take any prescription medication for blood pressure, heart disease, or erectile dysfunction.

The Science Behind CircO2: How Does It Work?

CircO2 is a nitric-oxide-support lozenge from Advanced Bionutritionals, the same Norcross, Georgia-based company behind Advanced Vision Formula (reviewed separately). Where Vision Formula is a “kitchen sink” antioxidant blend, CircO2 is narrower and more mechanistically focused: it’s built around boosting nitric oxide (NO), a signaling molecule that relaxes and widens blood vessels, via two complementary pathways: L-citrulline (which the body converts to L-arginine, a direct NO precursor) and beetroot extract (a dietary nitrate source that the body also converts to NO).

The product’s standout feature is delivery format: instead of a capsule or tablet swallowed and processed through the digestive tract, CircO2 is a lozenge meant to dissolve under the tongue. The company’s marketing ties this to research suggesting oral bacteria play a role in converting dietary nitrates into nitric oxide, a real area of physiology research, though the specific “this exact lozenge format gives you faster/better absorption than a capsule” claim is a product-positioning claim rather than something independently tested and published for this finished product.

A note on the marketing ecosystem around this product: while researching this review, several websites surfaced that present themselves as “official” CircO2 sites (separate from the real manufacturer site, advancedbionutritionals.com) using significantly more dramatic language, including phrases like “the youth molecule,” claims of restoring “the strength and vitality you deserve,” and fabricated-reading first-person testimonials attributed to named individuals. These are not the manufacturer’s own marketing and should be treated with real skepticism. They read as SEO/affiliate content rather than vendor-authored material, and the claims on them go well beyond what the FDA-disclaimer-compliant language on the actual manufacturer page states. This review is based on the real manufacturer’s site, not these secondary sources.

Intended Target Biometrics

• Circulation / vasodilation: the core mechanism, via L-citrulline and dietary nitrates
• Cardiovascular support: hawthorn berry extract, traditionally associated with heart and vascular health
• Energy / stamina: framed as a downstream effect of improved circulation and oxygen delivery, plus vitamin B12’s role in energy metabolism
• Secondary claims (per manufacturer and affiliate marketing): mental clarity, “sexual vitality”/performance, and general healthy aging support

Image credit: Advanced Bionutritionals

Image credit: Advanced Bionutritionals

Who Should Consider This Supplement (And Who Must Avoid It Entirely)

This is the most important section of this review. Based on the ingredient profile and well-established pharmacology (not a personalized medical assessment):

⚠️ Must consult a doctor before use, or likely should avoid entirely:

• Anyone taking PDE5 inhibitors for erectile dysfunction (sildenafil/Viagra, tadalafil/Cialis, vardenafil/Levitra). Combining nitric-oxide-boosting supplements with these medications carries a well-documented risk of severe, potentially dangerous drops in blood pressure. This combination is treated as an absolute contraindication in the same drug class as prescription nitrates.
• Anyone taking prescription nitrates (e.g., nitroglycerin) for angina or heart disease, for the same reason.
• Anyone on blood pressure medication generally. L-citrulline and dietary nitrates can have additive blood-pressure-lowering effects; combining them with antihypertensives can cause excessive drops in blood pressure, dizziness, or fainting.
• Anyone with unstable angina, a recent heart attack, or heart failure. Vasodilation from this category of supplement can worsen hemodynamic instability in these conditions; cardiology guidance is warranted before use.
• Pregnant or nursing individuals (not addressed on the label; default to caution given the blood-pressure effects).

This is not a minor caution to skim past. The product is explicitly marketed (in manufacturer and especially affiliate copy) to adults in their 50s, 60s, 70s, and 80s, precisely the population most likely to be on one or more of the medications above. Anyone in that situation should talk to a doctor or pharmacist before starting this product, not just check the bottle label.

May be worth discussing with a doctor for:

• Adults without the above conditions or medications who are interested in general circulation/energy support

Deep-Dive Ingredient & Dosage Breakdown

The product page describes the formula in aggregate rather than listing every individual ingredient amount in the marketing copy reviewed; specific milligram doses are only visible on the physical Supplement Facts panel (provided as an image link on the manufacturer’s site, not as accessible text). This review states plainly that a full, itemized public breakdown of doses was not available outside that label image.

L-Citrulline & Clinical Trial Notes

L-citrulline is reasonably well-studied as a nitric oxide precursor; clinical research has shown it can improve blood flow measures, including in older adults, and has documented blood-pressure-lowering effects. This is also the mechanistic basis for the medication interaction warning above: the same property that makes it potentially useful for circulation is what makes it risky in combination with vasodilator medications.

Beetroot Extract & Scientific Backing

Beetroot/dietary nitrate research is one of the more replicated areas in sports and cardiovascular nutrition. Multiple studies link beetroot supplementation to modest blood pressure reductions and improved exercise/circulatory measures. The dose in this specific product isn’t disclosed in the marketing copy reviewed.

Hawthorn Berry, Vitamin C, Vitamin B12, and Fillers/Excipients Check

• Hawthorn berry extract has a long traditional-medicine history for cardiovascular support, with some modern research on endothelial and heart-function effects; evidence quality varies and most studies are smaller and less definitive than the L-citrulline/beetroot research.
• Vitamin C is included partly for general antioxidant support and partly because it plays a role in nitrite-to-nitric-oxide conversion in acidic environments (e.g., the mouth), a real mechanism, though its specific contribution to this product’s effect isn’t independently quantified.
• Vitamin B12 supports energy metabolism and nerve health; its direct contribution to nitric oxide production specifically (as claimed in some marketing copy) is a thinner, less established claim than its general energy/nerve-health role.
• Per manufacturer and retail listings, the product is marketed as non-GMO, gluten-free, dairy-free, soy-free, and vegan — manufacturer/retailer claims rather than third-party-certified.

Manufacturing Standards & Purity Verification (Trust Signals)

Third-Party Lab Testing & Certificate of Analysis (COA) Status

As with Advanced Vision Formula, Advanced Bionutritionals does not publish a Certificate of Analysis or independent third-party lab test results for CircO2 on its public site. The company describes the same general in-house quality practices (supplier qualification testing, FTIR purity checks, USP disintegration testing) that apply across its product line: legitimate internal QC, but not independently verifiable by a customer.

Facility Certifications

The manufacturing facility is described as GMP-certified and FDA-registered, consistent with the rest of the company’s product line and standard for the supplement industry. As before, this confirms adherence to baseline manufacturing practices, not third-party potency or purity verification for this specific product.

What User Reviews Commonly Report

This section draws on the 1,618 publicly visible customer reviews on the manufacturer’s own product page (3.9/5 average, 74% “recommend” rate at time of writing) and on Trustpilot, where the company overall sits around 4.0 to 4.1/5 across several hundred reviews, alongside a notably less favorable picture on PissedConsumer.com (1.6/5 from 75 reviews) and recurring BBB complaint patterns. The contrast between these sources is itself worth noting: review platforms with a lower barrier to leaving a negative review (PissedConsumer, BBB) paint a meaningfully rougher picture than the manufacturer’s own on-site reviews.

This review does not use the “Eddie, 82” or similar anecdotes found in the company’s affiliate marketing materials. Those are unsourced, third-party-facing marketing copy provided for affiliates to use, not independently verifiable customer accounts, and using them would present an unsourced story as if it were a verified result.

General Timeline Reported by Users

Reviewers who report positive experiences commonly describe:

• A sense of increased energy or stamina, in some cases reported within the same day or within about 20 to 30 minutes of taking the lozenge. This is a fast subjective response that’s plausible given the sublingual delivery, though “feeling more energetic” isn’t the same as a measured physiological change
• Improved circulation sensations, particularly in the legs, reported over weeks to months of consistent use
• General “feeling stronger/more capable” framing, especially among older reviewers

A meaningful minority of reviews are short and non-specific (“great product,” “works well”), which limits how much can be drawn from them about mechanism or magnitude of effect.

Documented Minor Side Effects & Safety Precautions

Reported complaints in the research for this review centered more on packaging/shipping issues (e.g., damaged blister packs) than on adverse physical reactions to the product itself. No pattern of serious adverse events specific to CircO2 surfaced.

The safety issue that matters most here isn’t a “side effect” in the conventional sense. It’s the medication interaction risk detailed extensively above, which is a real pharmacological concern rather than an anecdotal complaint, and is the single most important piece of information in this review.

Separately, company-wide customer service complaints (not specific to CircO2) continue the pattern seen with Advanced Vision Formula: difficulty canceling auto-ship/subscription orders, reports of unauthorized upsell charges accepted (per the company’s own framing) during checkout that some customers say they didn’t intend to accept, and refund delays that in some documented cases took months and multiple follow-ups to resolve. This is a company-level pattern worth factoring into a purchase decision, separate from any assessment of the ingredients themselves.

Value Assessment: Cost Per Serving Breakdown

Pricing from the manufacturer’s official product page (advancedbionutritionals.com) at time of writing.

Shipping is free on the 3- and 6-box tiers. All tiers are listed as one-time payments on the product page reviewed, though as with Vision Formula, the company also operates an auto-ship program referenced elsewhere on its site — worth double-checking which option is selected at checkout, given the cancellation-friction complaints noted above.

This is a meaningfully premium price point relative to mass-market nitric oxide supplements, most of which run lower per serving for capsule or powder formats, though the lozenge delivery format and dual-pathway (citrulline + nitrate) approach are genuine differentiators worth weighing against the price.

The Balanced Verdict: Pros and Cons

Why We Recommend This Formulation (The Pros)

• Mechanistically sound, dual-pathway approach. Combining L-citrulline and dietary nitrates (beetroot) targets nitric oxide production through two distinct, independently-studied routes rather than relying on one.
• Sublingual lozenge format is a genuine point of differentiation from the capsule/powder formats that dominate this category, and is plausible on the physiology even though the specific “faster/better absorption” marketing claim isn’t independently verified for this product.
• Reasonably large, mostly positive on-site review base. 1,618 reviews is a substantial sample, and even with the lower 3.9/5 average (vs. Vision Formula’s 4.0), most feedback is positive.
• Same 90-day refund policy as the rest of the product line, at least on paper.
• Clean-label positioning (non-GMO, gluten-free, dairy-free, soy-free, vegan) for those avoiding common allergens.

The Drawbacks (The Cons: Real Safety Considerations, Price, and Transparency Gaps)

• The medication interaction risk is the standout concern for this specific product, more so than for most supplements reviewed under this framework. Anyone on PDE5 inhibitors, prescription nitrates, or blood pressure medication needs to treat this as a genuine medical question, not a label formality.
• No public third-party COA or lab verification, same gap as the rest of the company’s line.
• Premium pricing ($1.38 to $2.00/serving) relative to standard nitric oxide supplements in capsule or powder form.
• A noisy, sometimes misleading third-party marketing ecosystem surrounds this specific product. Multiple non-manufacturer websites use more aggressive, less compliant claims than the real manufacturer site does. Anyone researching this product should be careful to confirm they’re looking at official Advanced Bionutritionals material, not a lookalike site.
• Same company-wide customer service complaint pattern as noted for Vision Formula: auto-ship cancellation friction, occasional unauthorized upsell charges, and refund delays requiring follow-up.
• Incomplete public ingredient-dose transparency, with full amounts only visible on the physical label image rather than in accessible text.

Head-to-Head: CircO2 vs. HumanN Neo40 vs. Standard Beet Root / L-Citrulline Powder

How to read this table: CircO2’s main differentiation is the dual-pathway formula plus the lozenge format, which puts it in a similar conceptual category to other sublingual nitric oxide products like Neo40 rather than standard swallowed capsules. Price-wise it’s not dramatically out of line with other lozenge-format competitors, but it is more expensive than basic powder or capsule alternatives that deliver similar core ingredients (just citrulline, or just beetroot nitrate) without the lozenge delivery mechanism or secondary ingredients.

Alternative Formulations Worth Comparing

• HumanN Neo40 Daily: a comparable sublingual lozenge approach focused more narrowly on nitrate conversion; worth comparing directly if delivery format matters to you.
• Standard L-citrulline or beetroot powder/capsule supplements: meaningfully cheaper if you don’t need or want the lozenge format or the secondary ingredients (hawthorn, B12).
• N1O1 Nitric Oxide Lozenges: another sublingual-format competitor in this same niche, mentioned here as a category alternative to investigate further rather than independently verified in this research.

The same medication-interaction caution applies to all of these alternatives. This is a category-wide consideration tied to the core mechanism (nitric oxide / vasodilation), not something specific to this brand.

How This Review Was Researched

This review was compiled from Advanced Bionutritionals’ official product and quality pages, the company’s Digistore24 affiliate-program materials, publicly visible customer reviews on the manufacturer’s site and on Trustpilot/PissedConsumer/BBB, general medical and pharmacological literature on nitric-oxide-boosting supplement interactions, and independent retail listings (Amazon, Walmart) for both this product and comparison products. No sample of CircO2 was provided or tested firsthand, and no clinical trial of this specific finished formula was located; ingredient-level and interaction research cited above refers to the ingredients and supplement category generally, not to this specific product as tested in isolation. Several third-party websites presenting more dramatic marketing claims for this product were identified during research and explicitly excluded as unreliable sources for this review.

Final Purchasing Recommendation & Secure Order Channels

CircO2 is a reasonably well-constructed nitric oxide supplement built on two legitimately studied mechanisms (L-citrulline and dietary nitrate), in a differentiated lozenge format, from a manufacturer with a large (if mixed) review history. The ingredients themselves aren’t the main concern here.

The main thing to take away from this review is the medication interaction risk. If you, or the person you’re buying this for, take medication for erectile dysfunction (sildenafil, tadalafil, vardenafil), prescription nitrates for heart disease, or blood pressure medication generally, talk to a doctor or pharmacist before starting this product. This isn’t precautionary boilerplate — it’s a real and well-documented pharmacological interaction, and the product’s marketed demographic (older adults, often managing exactly these conditions) makes this more relevant than for many other supplements in this category. Beyond that, the same transparency gap (no public COA) and customer-service friction pattern (auto-ship cancellation, refund delays) that applies to the rest of Advanced Bionutritionals’ line applies here too.

Order through the manufacturer’s official secure store; not one of the third-party lookalike domains identified in this review. You can use the “View Offer” button provided in the review.

Editor’s Summary

CircO2

Sublingual nitric oxide support lozenge combining L-citrulline and beetroot extract with hawthorn berry, vitamin C, and B12. Made by Advanced Bionutritionals.

Product Brand: Advanced Bionutritionals

Editor's Rating:
3.5

Pros

• Mechanistically sound, dual-pathway approach combining L-citrulline and dietary nitrate.
• Sublingual lozenge format is a genuine differentiator from capsule and powder competitors.
• Large, mostly positive on-site review base of 1,618 reviews.
• Same 90-day refund policy as the rest of the product line.
• Clean-label positioning: non-GMO, gluten-free, dairy-free, soy-free, vegan.

Cons

• Significant medication interaction risk for anyone on PDE5 inhibitors, prescription nitrates, or blood pressure medication.
• No public third-party Certificate of Analysis or lab verification.
• Premium pricing relative to standard nitric oxide supplements.
• Noisy third-party marketing ecosystem with misleading lookalike sites.
• Company-wide pattern of auto-ship cancellation and refund-delay complaints.
• Full ingredient dosages not disclosed outside the physical label image.

Frequently Asked Questions