CircO2 Review (2026): Does This Sublingual Nitric Oxide Lozenge Work?

Most nitric oxide supplements come in the same format: a capsule you swallow, digest, and hope enough of the active ingredient survives to actually reach your bloodstream. CircO2, made by Advanced Bionutritionals, takes a different approach — a fast-dissolving lozenge you place under your tongue instead of swallowing.

We looked into whether that delivery method is a genuine advantage or just a marketing angle, and how the formula compares to standard nitric oxide capsules like Nitric Boost.

What is CircO2?

CircO2 is a daily nitric oxide support supplement sold as quick-dissolve tablets (30 per box), rather than the capsules or powders most competitors use. The company's central claim is that nitric oxide production actually begins in the mouth — via oral bacteria on the tongue — and that a sublingual lozenge can raise nitric oxide levels faster than something that has to pass through the stomach first.

It's endorsed by Dr. Greg Eckel, a naturopathic physician (not a medical doctor) with over 20 years in integrative medicine, who is a paid spokesperson for the brand — disclosed directly on the product page.

Product Summary

The Science: Why the Lozenge Format Matters

Standard nitric oxide capsules containing L-arginine face a well-documented problem: clinical research shows a large share of oral L-arginine is broken down during digestion before it ever reaches the bloodstream, and first-pass liver metabolism further reduces what's left.

CircO2 sidesteps this by using a fast-dissolving lozenge instead of a capsule. The active compounds absorb through the tissue under the tongue, entering the bloodstream directly rather than going through the stomach and liver first. This is a legitimate pharmacological principle — sublingual delivery is used in real medicine (nitroglycerin tablets for angina, for example) specifically because it's faster and more reliable than oral digestion for certain compounds.

• Beet Root Powder: A well-established source of dietary nitrates, which the body converts into nitric oxide. Commonly used in sports nutrition for endurance and blood flow support.
• Hawthorn Berry: Traditionally used for cardiovascular support; the brand positions it here as an absorption enhancer for the other ingredients.
• L-Citrulline: Notably, CircO2 uses L-citrulline instead of L-arginine. This lines up with a reasonable body of research suggesting citrulline converts to nitric oxide more efficiently than arginine, particularly in men over 45 — likely why the formula skips arginine altogether rather than combining both.
• Vitamin B12, Vitamin C, Magnesium: Foundational nutrients that support energy metabolism, protect nitric oxide from oxidative breakdown, and support healthy blood vessel function.

What CircO2 Claims to Help With

Per the manufacturer, users report improvements in: daily energy and stamina, mental clarity, blood pressure readings already within a normal range, joint comfort (via improved circulation), intimacy and performance, and sleep quality. These are testimonial-based claims, not clinical trial results specific to this exact formula — treat them as anecdotal rather than guaranteed outcomes.

When to See a Doctor First

CircO2 is designed to support healthy circulation and everyday energy — not to treat diagnosed cardiovascular disease. If you take blood pressure medication, nitrate medication, or a PDE5 inhibitor (Viagra, Cialis), talk to your doctor before starting any nitric oxide supplement, since combining these with vasodilating ingredients can cause an unsafe drop in blood pressure. Anyone with chest pain, shortness of breath, or an irregular heartbeat should see a doctor rather than trying a supplement first.

Pricing and Guarantee

CircO2 is sold directly through Digistore24 checkout, not in retail stores:

• 1 Box (30-day supply): $49.95
• 3 Boxes (90-day supply): $44.95/box — $134.85 total, free shipping
• 6 Boxes (180-day supply): $41.50/box — $249.00 total, free shipping

Every order is covered by a 90-day "down to the last lozenge" money-back guarantee — you can return the box even if it's empty.

Frequently Asked Questions (FAQ)

1. Is CircO2 better than capsule-based nitric oxide supplements? It depends on what you value. The sublingual format has a real absorption advantage in theory, since it skips digestion. Whether that translates to noticeably better results than a well-formulated capsule (like ones combining L-citrulline, beetroot, and antioxidants) hasn't been tested head-to-head in independent clinical trials — so we'd call it a legitimate alternative rather than a definitive upgrade.

2. Does CircO2 contain caffeine or stimulants? No. It's formulated around vasodilation (blood flow) rather than central nervous system stimulation, so it shouldn't cause jitters.

3. How is the real 3.9/5 rating different from other reviews you've published? Most direct-to-consumer supplement pages either hide review data or only show curated 5-star testimonials. CircO2's page publishes an aggregate rating (3.9/5 from 1,618 reviews) directly, which we think is a meaningfully more honest signal than a wall of unverifiable quotes — even though it's a more modest number.

4. Who endorses CircO2, and is that endorsement paid? Dr. Greg Eckel, a naturopathic physician, endorses the product. Advanced Bionutritionals discloses on the sales page that he is compensated for this endorsement — worth knowing when you weigh how much to factor his opinion in.

5. Where can I buy CircO2? CircO2 is sold exclusively through the official website via Digistore24 checkout — it isn't available in stores or on Amazon.

Scientific References

1. Bailey, S. J., et al. (2009). Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. Journal of Applied Physiology, 107(4), 1144-1155.
2. Schwedhelm, E., et al. (2008). Pharmacokinetics and pharmacodynamics of L-citrulline and L-arginine supplementation in healthy adult men. British Journal of Clinical Pharmacology, 65(1), 51-59.
3. Ignarro, L. J., et al. (2006). Nitric oxide as a unique signaling molecule in the cardiovascular system. Circulation Research, 99(8), 819-831.

Maximize Your Results: Regular cardiovascular exercise is one of the few habits proven to improve endothelial function and support your body's own nitric oxide production — a few sessions of brisk walking, cycling, or resistance training each week can compound the circulation benefits you're after with CircO2.