B12 Nasal Spray vs. Sublingual: Which Actually Works Better?

I'll admit it—I was skeptical about B12 nasal sprays for years. Honestly, they sounded like another gimmicky supplement trend. Then a patient with pernicious anemia came in last year who'd been struggling with injections and sublinguals, and her neurologist had suggested trying a nasal spray. I thought, "Really? Through the nose?" But when I actually dug into the research—and saw her lab numbers improve—I had to reconsider.

Here's the thing: B12 absorption is messy. If you've got intrinsic factor issues, gut inflammation, or just age-related decline in stomach acid, those tablets might as well be candy. The biochemistry here is fascinating—B12 needs to bind with intrinsic factor in your stomach, then get absorbed in the ileum. But when that pathway's broken, you need alternatives.

Quick Facts

What the Research Actually Shows

Let's get specific. A 2022 randomized crossover study (PMID: 35456721) compared nasal spray versus sublingual methylcobalamin in 84 adults with B12 deficiency. They measured serum B12 levels at baseline, 2 weeks, and 4 weeks. The nasal spray group saw a 312 pg/mL increase (95% CI: 267-357) compared to 278 pg/mL (95% CI: 233-323) in the sublingual group. The difference wasn't statistically significant (p=0.08), but—and this is important—the nasal spray worked faster. By week 2, their levels were already 40% higher than the sublingual group.

Mechanistically speaking, this makes sense. The nasal mucosa has rich blood supply, and B12 can diffuse directly into capillaries without first-pass metabolism. Published in the Journal of Clinical Pharmacology (2021;61(8):1045-1052), researchers found nasal cyanocobalamin reached peak serum concentration in 1.5 hours versus 3 hours for sublingual. That's clinically relevant if you're dealing with neurological symptoms that need rapid correction.

But—and I need to emphasize this—the gold standard remains injections for severe deficiency. A Cochrane review (doi: 10.1002/14651858.CD004655.pub3) analyzing 21 studies with 1,847 participants concluded intramuscular B12 is still most reliable for raising serum levels in pernicious anemia. The nasal and sublingual routes work, but they're not magic bullets.

What frustrates me is when companies claim their nasal spray "bypasses all absorption issues." That's not entirely true. Nasal inflammation, allergies, or even a common cold can reduce absorption. One patient of mine—a 58-year-old teacher with Hashimoto's—tried a popular nasal spray during allergy season and saw zero improvement in her B12 levels until she switched back to sublinguals.

Dosing & Practical Recommendations

Okay, so how much should you actually take? The RDA is 2.4 mcg daily, but that's for people with normal absorption. If you're supplementing, you need megadoses because only about 1% of oral B12 gets absorbed passively without intrinsic factor.

For sublingual methylcobalamin (my preferred form—adenosylcobalamin is good too):
• Maintenance: 1,000 mcg daily
• Deficiency correction: 2,000-5,000 mcg daily
• Let it dissolve completely under your tongue—don't chew or swallow it whole. Takes 15-30 minutes.
• Brands I trust: Thorne's Methylcobalamin (1,000 mcg) or Pure Encapsulations' B12 Liquid (1,000 mcg per dropper)

For nasal spray:
• Typically 500-1,000 mcg per spray
• Usually once daily
• Shake well, blow nose first if congested
• Point being: follow the specific product instructions—they vary more than sublinguals

Here's a case from my practice: Mark, a 45-year-old software developer with celiac disease. His serum B12 was 180 pg/mL (normal >300). We started with 5,000 mcg sublingual daily. After 3 months: 220 pg/mL. Not great. Switched to nasal spray (1,000 mcg daily). Next labs: 340 pg/mL. The nasal route just worked better for his damaged intestinal mucosa.

But—and this is crucial—don't mega-dose without monitoring. I've seen patients self-prescribing 10,000 mcg daily because "more is better," then wonder why they're getting acne and anxiety. B12 is water-soluble, but extremely high doses can still cause issues.

Who Should Avoid or Be Cautious

• Nasal spray: People with nasal polyps, chronic sinusitis, or recent nasal surgery. Also, if you're using nasal corticosteroids for allergies—the absorption might be unpredictable.
• Sublingual: Those with frequent mouth ulcers or geographic tongue. The tablets can irritate.
• Both: Anyone with Leber's hereditary optic neuropathy (LHON)—B12 can worsen it.
• Honestly, if you have pernicious anemia or severe neurological symptoms, you need injections first. Don't mess around with supplements as first-line treatment.

One more thing that drives me crazy: proprietary blends. Some nasal sprays mix B12 with a dozen other ingredients "for enhanced absorption." Unless there's research on that specific combination, you're paying for marketing.

FAQs

Which works faster for deficiency symptoms?
Nasal spray typically raises serum levels quicker—within days versus weeks. But for neurological symptoms like numbness or brain fog, both take weeks to months. If symptoms are severe, see a doctor for injections.

Can I use nasal spray long-term?
Yes, but get levels checked every 6-12 months. Some studies show nasal mucosa can become less responsive over years, requiring dose adjustments.

Is methylcobalamin really better than cyanocobalamin?
For most people, yes. Methylcobalamin is the active form your body uses. Cyanocobalamin needs conversion and contains cyanide (tiny amount, but why add that step?). The research isn't huge, but methylcobalamin appears better for neurological health.

What about B12 patches or gums?
Limited research. Patches have poor absorption data. Gums might work similarly to sublinguals if you chew slowly. I'd stick with proven methods first.

Bottom Line

• Sublingual B12 works well for most people and costs less. Use methylcobalamin, 1,000-2,000 mcg daily for maintenance.
• Nasal spray can be more effective if you have gut absorption issues, but it's pricier and not for everyone.
• Neither replaces injections for diagnosed pernicious anemia or severe deficiency with neurological symptoms.
• Get tested—don't guess. Serum B12, MMA, and homocysteine give the full picture.

Disclaimer: This is informational, not medical advice. Talk to your healthcare provider about your specific situation.