First, a correction: B-12 is not a peptide. It's an essential vitamin — a cobalt-containing nutrient your body needs for healthy blood cells, nerves, and DNA. It's genuinely valuable when someone is deficient, and there are FDA-approved injectable products for that. But it is not a magic energy shot for people who already have normal B-12, and it should never be marketed as an unapproved "research peptide."
B-12/cobalamin is a water-soluble corrinoid cofactor used clinically to correct deficiency from dietary insufficiency, malabsorption, autoimmune gastritis/pernicious-anemia states, GI surgery, and medication-associated risk. Oral high-dose therapy and IM/deep-SC injections can both correct deficiency in many contexts, but severe neurologic disease, major malabsorption, or uncertain diagnosis requires clinician-directed evaluation.
Cobalamin biology centers on two active coenzyme forms: methylcobalamin for cytosolic methionine synthase and adenosylcobalamin for mitochondrial methylmalonyl-CoA mutase. Deficiency disrupts one-carbon metabolism, homocysteine remethylation, folate recycling, DNA synthesis, methylmalonic-acid metabolism, erythropoiesis, and neurologic/myelin maintenance. Cyanocobalamin (CAS 68-19-9; C₆₃H₈₈CoN₁₄O₁₄P; 1355.4 Da; 4.34% cobalt) is the synthetic supplement form.
B-12 is the atlas's deliberate category outlier: it isn't a peptide at all, but a cobalt-containing corrinoid vitamin and a genuinely FDA-approved drug. Its honest picture has two halves. For confirmed or high-risk deficiency — dietary insufficiency, malabsorption, pernicious anemia, GI surgery, certain medications — replacement therapy has strong, long-established evidence (Grade A/B), and there's an approved high-dose cyanide antidote (hydroxocobalamin, a related but distinct molecule). For the "B-12 energy shot" sold to people with normal B-12, the evidence is weak: it corrects deficiency-related fatigue but is not a proven stimulant or performance enhancer. The page keeps a hard wall between those two, and flags the classic clinical trap — giving folate alone can fix the anemia while neurologic B-12 injury silently progresses.
B-12's biology is unusually clean to state: the body converts it into two active coenzyme forms, each running one critical reaction. Methylcobalamin is the cofactor for methionine synthase (the link between the folate cycle and methylation/DNA synthesis), and adenosylcobalamin is the cofactor for methylmalonyl-CoA mutase (a mitochondrial step in fat/amino-acid breakdown). When B-12 is missing, both reactions stall — folate gets trapped, DNA synthesis falters (megaloblastic anemia), homocysteine and methylmalonic acid rise (the functional biomarkers), and myelin maintenance suffers (neurologic injury). This is established biochemistry, so the mechanism grades are genuinely high (A/B) — a contrast to the gray-market peptides, where mechanism is mostly hypothesis. The one separate mechanism is hydroxocobalamin's cyanide binding, an approved toxicology use.
| Coenzyme | Enzyme | Reaction | Biomarker if low |
|---|---|---|---|
| Methylcobalamin | Methionine synthase | Homocysteine → methionine | ↑ Homocysteine |
| Adenosylcobalamin | Methylmalonyl-CoA mutase | Methylmalonyl-CoA → succinyl-CoA | ↑ MMA |
| Form | Role |
|---|---|
| Cyanocobalamin | Stable synthetic supplement/injection form |
| Hydroxocobalamin | Injection form + cyanide antidote (distinct molecule) |
| Methylcobalamin | Active coenzyme (methionine synthase) |
| Adenosylcobalamin | Active coenzyme (MMA mutase) |
Unlike the research peptides elsewhere in the atlas, B-12 has legitimate FDA-approved drug products with labeled dosing. The approved use is correcting deficiency — injectable cyanocobalamin for malabsorption/pernicious-anemia states, and high-dose oral for many other contexts. The working unit is micrograms. The honest split: deficiency replacement is Grade A/B (approved label plus long practice), oral-vs-IM equivalence is real but rests on low-quality Cochrane evidence (Grade B), and the "wellness B-12 shot" in non-deficient people is Grade D/P. Hydroxocobalamin IV for cyanide poisoning (5 g) is a completely separate emergency antidote — not wellness dosing. The calculator below does µg-from-injection math; most prescription cyanocobalamin is supplied as a ready-to-use 1000 mcg/mL solution, not a lyophilized peptide vial.
| Band | Dose | mcg/kg/day @ 70 kg | Basis |
|---|---|---|---|
| Nutritional RDA | 2.4 mcg/day | 0.034 | Normal requirement (not treatment) |
| Low supplement | 25–100 mcg/day | 0.36–1.43 | General supplementation |
| Oral replacement | 1000 mcg/day | 14.3 | Deficiency oral replacement |
| High oral | 2000 mcg/day | 28.6 | RCT/review protocols |
| Labeled injection | 100 mcg/day IM | 1.43 | Cyanocobalamin label |
| Cyanide antidote | 5 g IV (hydroxo) | ~71,400 (single) | CYANOKIT (emergency only) |
| Body weight | 1000 mcg/day oral | mcg/kg/day | 2000 mcg/day |
|---|---|---|---|
| 55 kg | 1000 mcg | 18.2 | 2000 mcg |
| 75 kg | 1000 mcg | 13.3 | 2000 mcg |
| 95 kg | 1000 mcg | 10.5 | 2000 mcg |
| 105 kg | 1000 mcg | 9.5 | 2000 mcg |
Most protocols use fixed doses, not weight-based dosing — this table is for modeling only.
| Trigger | Action | Rationale |
|---|---|---|
| Severe neurologic symptoms or very low B-12 | Clinician-directed parenteral replacement / urgent eval | Prevent irreversible neurologic injury |
| Macrocytic anemia, suspected B-12 deficiency | Treat B-12 + evaluate folate/iron; monitor CBC/retic | B-12 deficiency can mimic folate deficiency |
| B-12 improves but MMA/homocysteine stay high | Reassess renal function, adherence, dose, diagnosis | MMA/homocysteine functional but not perfectly specific |
| Hypokalemia during rapid anemia correction | Hold / escalate monitoring | Label warns potassium/platelet monitoring in severe megaloblastic anemia |
| Rash, swelling, wheeze, hypotension after injection | Hard stop + urgent evaluation | Parenteral hypersensitivity/anaphylaxis reported |
| No deficiency/risk, using for "energy" | De-escalate; avoid repeated injections as default | Benefit outside deficiency is not established |
| Marker | Validated for deficiency? | For "wellness optimization"? |
|---|---|---|
| Serum B-12 | Yes (imperfect) | No |
| CBC / MCV | Yes | No |
| Reticulocyte count | Yes (early response) | No |
| MMA | Yes (with caveats) | No |
| Homocysteine | Yes (nonspecific) | No |
| Intrinsic-factor antibody | Yes (pernicious anemia) | No |
| Mechanism | Detail |
|---|---|
| Intrinsic-factor pathway | Saturable; limited in PA |
| Passive diffusion | ~1% of high oral dose absorbed without IF |
| Claim | Reality |
|---|---|
| Sublingual > oral | Comparable, not clearly superior |
| Aspect | Detail |
|---|---|
| Form | Hydroxocobalamin (≠ cyanocobalamin) |
| Dose scale | Grams, not micrograms |
| Mechanism | Binds cyanide → cyanocobalamin |
| If you are… | Likely effect |
|---|---|
| Deficient | Real benefit (corrects deficiency) |
| Not deficient | No proven energy/performance benefit |
B-12 is dosed in micrograms. Most prescription cyanocobalamin is supplied as a ready-to-use 1000 mcg/mL sterile solution — not a lyophilized peptide vial — so this calculator typically just converts a target dose to a draw volume. It's clinical-reference math, not a self-dosing recommendation; deficiency treatment belongs under clinician care.
For B-12, the meaningful "combinations" aren't performance stacks — they're the cofactors and risk-contexts that belong in a proper deficiency workup. B-12 and folate are intertwined in one-carbon metabolism, which creates the single most important rule on this page: never give folate alone when B-12 deficiency is possible, because folate can correct the anemia while neurologic injury silently progresses. Iron is often co-evaluated in mixed anemia; B6/folate are homocysteine-pathway partners (though lowering homocysteine doesn't guarantee outcome benefit); and metformin/PPI use are recognized deficiency-risk contexts to monitor rather than reflexively inject. The hard constraint: don't use B-12 shots to bypass evaluation of anemia, neuropathy, or autoimmune gastritis.
| Scenario | Rule |
|---|---|
| Folate alone | Masks anemia, not neuro injury |
| Exclude B-12 first | Always |
| Context | Action |
|---|---|
| Mixed anemia | Check iron studies |
| Effect | Caveat |
|---|---|
| ↓ Homocysteine | ≠ proven CV benefit |
| Drug | Approach |
|---|---|
| Metformin / PPI | Monitor, then treat if low |
B-12 has an excellent safety profile: it's water-soluble, excess is largely excreted, and there's no established toxic upper level, which is why it's available OTC. But "very safe" isn't "no cautions." Parenteral B-12 has rare but real hypersensitivity/anaphylaxis reports, and the product label lists serious reactions (pulmonary edema, vascular thrombosis) plus the hypokalemia risk during rapid correction of severe megaloblastic anemia. The most important safety issues are diagnostic rather than toxicological: the folate-masking trap (treating the wrong deficiency lets neurologic injury progress), the historical caution in Leber hereditary optic neuropathy with cyanocobalamin, and the temptation to use "energy shots" to paper over an undiagnosed problem.
B-12 itself rarely harms anyone — the real risks come from what a B-12 shot lets you skip. The folate-masking trap is the classic example: correct the anemia, miss the cause, and let neurologic injury become permanent. The safe approach is to diagnose before treating, not to inject and hope.
Anaphylaxis to injectable B-12 is uncommon but documented, and the label lists serious cardiovascular reactions. That's a reason injections belong in a supervised setting for genuine indications — not as a casual repeated "wellness" ritual where the risk-benefit no longer favors the needle.
When B-12 reverses a severe megaloblastic anemia, the sudden surge in red-cell production can pull potassium into new cells and cause hypokalemia. This is a known, monitorable effect — one of the few times B-12 treatment itself needs active lab follow-up.
| Condition / scenario | Concern | Severity |
|---|---|---|
| Known cobalt/cobalamin hypersensitivity | Injection reaction / anaphylaxis risk | High |
| Leber hereditary optic neuropathy | Cyanocobalamin optic-nerve caution | High |
| Severe megaloblastic anemia | Rapid correction → potassium/platelet monitoring | High |
| Unexplained neurologic symptoms | Needs diagnosis, not a casual supplement protocol | High |
| Suspected folate deficiency | Folate/B-12 interaction can obscure diagnosis | Moderate |
| Renal disease | MMA interpretation can be confounded | Moderate |
| Polycythemia vera / thrombosis history | Label lists PV/thrombosis concern | Moderate |
| Pregnancy / lactation | Treat deficiency, but clinician-guided | Moderate |
| Athletic competition with IV infusions | Substance permitted, but IV-method rules may apply | Caution |
| "Energy shot" use without deficiency | Benefit uncertain; may delay real diagnosis | Caution |
B-12's evidence base is the inverse of the gray-market peptides: the core use is genuinely well-supported, and the marketing claims are the weak part. Treating real deficiency and established malabsorption states rests on decades of clinical practice and an approved label (Grade A/B). The interesting modern evidence question is route — and here Cochrane and several RCTs show oral high-dose B-12 can normalize serum B-12 comparably to IM, though the trials are small and graded low/very-low quality. The biochemistry (methionine synthase, methylmalonyl-CoA mutase) is textbook-established (Grade A/B). What's weak is the "B-12 shot for energy/performance in non-deficient people" — that has essentially no supporting evidence, and the page grades it accordingly.
The prescribing information defines B-12's approved role: injectable cyanocobalamin for deficiency from malabsorption states (pernicious anemia, GI surgery, fish tapeworm, pancreatic/bowel malignancy), with the 100 mcg induction regimen, urinary-excretion PK, anaphylaxis warning, and the folate-masking caution. The regulatory backbone of the page.
A current clinical guideline on diagnosing and managing B-12 deficiency, covering when to test, how to interpret imperfect biomarkers, route selection, and follow-up — the kind of evidence-graded source that anchors the deficiency-treatment claims at Grade A, updating earlier cobalamin/folate disorder guidelines.
The authoritative mechanism and requirements reference: the methionine-synthase and methylmalonyl-CoA-mutase cofactor roles, the 2.4 mcg/day adult RDA, absorption physiology (intrinsic factor), and risk groups. The established biochemistry behind the Grade-A/B mechanism nodes.
A systematic review of RCTs comparing oral and IM B-12, concluding low-quality evidence that they have similar effects on normalizing serum B-12 and very-low-quality evidence for comparable safety — the basis for "oral can work, but the evidence base is thin."
A clinical review supporting oral 1000 mcg/day as a viable replacement for pernicious anemia with appropriate monitoring — important because PA was long considered a strict IM-only indication, and this reframes route choice.
A dose-finding trial in older adults with mild deficiency that found doses far above the RDA (>200× RDA) were needed to normalize deficiency markers — useful evidence that "RDA-sized" supplements don't treat established deficiency.
A systematic review comparing sublingual and oral B-12 against IM injections — supporting comparable efficacy rather than the "sublingual is superior" marketing claim, and informing the route-equivalence framing.
A clinical study in which 88.5% of pernicious-anemia patients were no longer deficient after one month of oral B-12, with improved biomarkers — recent evidence reinforcing oral replacement as a real option with monitoring.
The approved label for high-dose IV hydroxocobalamin as an antidote for known/suspected cyanide poisoning (5 g, optional second 5 g) — a genuinely approved emergency-toxicology use of a distinct cobalamin form, separate from B-12 replacement.
A historical review of B-12's discovery — the anti-pernicious-anemia factor crystallized in 1948, its structure solved by Dorothy Hodgkin's crystallography (Nobel work), and the later Woodward/Eschenmoser total synthesis. Context for one of the landmark molecules of 20th-century biochemistry.
Because B-12 isn't a peptide, the useful comparison is among its own forms, which are not interchangeable in role. Cyanocobalamin is the stable synthetic supplement/injection workhorse; hydroxocobalamin is both an injection form and the approved cyanide antidote (a distinct molecule dosed in grams, not micrograms); and methylcobalamin and adenosylcobalamin are the two active coenzymes the body actually uses. Marketing often implies the "active forms" are clinically superior supplements, but for correcting deficiency the evidence mostly supports comparable efficacy. The table keeps the approval reality honest — cyanocobalamin injection and CYANOKIT are FDA-approved; the methyl/adenosyl supplement forms vary by market.
| Compound | Primary use | Mechanism class | Evidence tier | Route | Regulatory status |
|---|---|---|---|---|---|
| B-12 / cyanocobalamin | B-12 deficiency replacement | Corrinoid vitamin cofactor | A/B for deficiency | Oral, IM, deep SC | FDA-approved injectable |
| Hydroxocobalamin | Deficiency (some markets); cyanide antidote | Corrinoid; cyanide binder | A/D for cyanide poisoning | IM or IV | CYANOKIT approved (cyanide) |
| Methylcobalamin | Supplement / replacement form | Active coenzyme (methionine synthase) | B/D by indication | Oral/sublingual/injection (varies) | Often supplement / varies |
| Adenosylcobalamin | Supplement / replacement form | Active coenzyme (MMA mutase) | P/D as supplement | Oral / supplement | Supplement / varies |
Because B-12 is not a peptide, these are related compounds — the cofactors and partners that share its metabolic neighborhood — rather than related peptides.
Evidence grades reflect the strength of support for the specific claim cited, not the prestige of the journal. B-12 is the rare atlas entry that earns multiple Grade-A sources — but honestly: the FDA label, NICE guideline, NIH fact sheet, and CYANOKIT label are A because they back genuinely approved/established uses (deficiency replacement, the cyanide antidote, the textbook biochemistry). The route-comparison and pernicious-anemia oral-replacement evidence is Grade B (real RCTs/reviews, but low/very-low quality by Cochrane). Identity and historical records are A/D. There is no high-grade source for "B-12 energy shots in non-deficient people," which is why that use is graded D/P throughout. The grade pattern makes the page's core point visible: strong evidence for treating real deficiency, weak evidence for the wellness marketing.