Methylcobalamin vs cyanocobalamin: which is better
Cyanocobalamin is stable, cheap, and used in most of the research. Methylcobalamin is already active. For topping up a dietary gap, the evidence that one beats the other is thinner than the internet suggests.
Written by R. Kessler · How we source this
Both methylcobalamin and cyanocobalamin raise blood B12 in people who are short on it. Cyanocobalamin is cheaper and is the form nearly all of the research used. Methylcobalamin is already active, so it skips a conversion step. For a healthy adult topping up a dietary gap, the evidence that one clearly beats the other is thin.
If cost matters, cyanocobalamin is the studied, stable choice. If you have a known conversion issue or simply prefer the active form, methylcobalamin is a reasonable preference rather than a proven upgrade. Keel uses methylcobalamin at 525 mcg.
What are the two forms, chemically?
Cyanocobalamin is a synthetic, stable form that the body converts into the two active coenzyme forms, methylcobalamin and adenosylcobalamin. The conversion involves stripping a cyanide group, which sounds alarming and is not: the amount is trivial next to the cyanide in ordinary food.
Methylcobalamin is already one of the active forms. It skips the conversion step, which is the entire basis of the claim that it is better. The step is not rate-limiting in healthy people, which is why the practical difference is smaller than the marketing suggests.
Which differences actually matter?
| Cyanocobalamin | Methylcobalamin | |
|---|---|---|
| Stability | Excellent, which is why it dominates research | Good, slightly less stable |
| Cost | Low | Higher |
| Conversion needed | Yes, into the active forms | No, already active |
| Research base | Most of the long-running trials | Smaller, mostly comparisons rather than outcome trials |
| Raises blood B12 | Yes | Yes |
| Sublingual advantage | None demonstrated | None demonstrated |
The last row is worth stating plainly. Sublingual B12 is marketed on the idea that absorption bypasses the gut, and B12 is absorbed in the ileum through intrinsic factor regardless of where it dissolves. A large oral dose works because a small percentage is absorbed by passive diffusion, not because of where it sits in your mouth.
Why do B12 labels carry enormous numbers?
Absorption through intrinsic factor saturates at roughly 1.5 to 2 mcg per dose. The adult reference intake is 2.4 mcg a day. So why does a capsule carry 500 or 1,000 mcg?
Because above the saturation point, a small fixed percentage of the remaining dose is absorbed passively. A big number on the label is a design decision that works with that mechanism, not a typo and not a boast. It is also why taking more and more does not scale linearly: the passive fraction stays small.
Does the B12 form matter on a GLP-1?
No study has shown that semaglutide or tirzepatide depletes B12 directly. What changes is intake, because eating far less food means less B12 arriving with it, and metformin, which many people on these medications also take, has a much better documented association with lower B12.
If you take metformin or a proton pump inhibitor, or you are vegan or vegetarian, B12 is worth a specific conversation with your prescriber rather than a decision made from a bottle. A serum B12 test, sometimes with methylmalonic acid if the result is borderline, is what actually answers the question.
Who should pick which?
- Topping up a dietary gap, healthy adult. Either works. Cyanocobalamin is the studied, stable, cheaper option.
- Known conversion difficulty, or a preference for active forms. Methylcobalamin, as a reasonable preference rather than a proven upgrade.
- Already tested and diagnosed deficient. Your clinician sets the dose and the route. Some people need injections, particularly with pernicious anaemia or after certain bowel surgeries, and that is a prescriber's call.
What is in our bottle?
Keel carries 525 mcg of methylcobalamin, alongside 400 mcg of folate as L-5-MTHF and 26 mg of B6 as P5P, all in the active forms, in one two-capsule serving with food. The whole label is on the B12 ingredient page, and the methylated trio is written up in methylated B12, folate and B6.
The wider picture is in our guide to eating and supplementing well on GLP-1 medications.
FAQ
Is methylcobalamin better than cyanocobalamin? For people with a specific conversion problem, possibly. For a healthy adult topping up a dietary gap, the evidence that it is clearly better is thin, and both raise blood B12.
Does the cyanide in cyanocobalamin matter? No. The amount released during conversion is trivial compared with the cyanide compounds present in ordinary food, and it has not been shown to be harmful at supplemental doses.
Should I take B12 sublingually? There is no demonstrated advantage. B12 is absorbed in the ileum through intrinsic factor regardless of where it dissolves, and a large swallowed dose works through passive diffusion.
How much B12 should I take on a GLP-1? Ask your prescriber, because the answer depends on your blood level and your other medicines. The adult reference intake is 2.4 mcg a day, and supplements supply far more for the passive-diffusion reason above.
Sources
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.
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