Vitamin B12 (cobalamin) is a vitamin your body cannot make on its own. Compounded vitamin B12 is a prescription preparation of B12 — usually as methylcobalamin or hydroxocobalamin — prepared by a licensed pharmacy as a sterile injection or as a nasal spray, at the strength your prescriber orders.
Vitamin B12 replacement itself is not experimental. For people who are genuinely deficient, it is one of the better-established treatments in medicine. What is compounded here is the form and the presentation — preservative-free vials and syringes, higher concentrations, and forms of B12 that no company markets as an FDA-approved drug in the United States.
How does it work?
Vitamin B12 is a cofactor for two enzymes — methionine synthase and L-methylmalonyl-CoA mutase — and the National Institutes of Health describes it as required for “development, myelination, and function of the central nervous system; healthy red blood cell formation; and DNA synthesis” (NIH Office of Dietary Supplements). When B12 runs low, red blood cells are made poorly (megaloblastic anemia) and nerves can be damaged.
Normally B12 from food is absorbed in the last part of the small intestine, and that step requires a stomach protein called intrinsic factor. Injections and nasal sprays bypass that pathway entirely, which is why they are used when absorption through the gut is the problem. Once B12 is replaced, the body draws on it as a cofactor again; it does not act as a stimulant, and it does not add energy to a body that already has enough B12.
What is it used for?
Vitamin B12 is prescribed to treat and prevent vitamin B12 deficiency. Common reasons a prescriber orders it include:
- Pernicious anemia — an autoimmune condition in which the stomach stops making intrinsic factor, so B12 cannot be absorbed from food
- Malabsorption — Crohn's disease, celiac disease, small bowel resection, or other gastrointestinal conditions
- After bariatric surgery — gastric bypass and similar procedures reduce the cells that make stomach acid and intrinsic factor
- Medication-associated deficiency — long-term metformin, proton pump inhibitors, or H2 blockers can interfere with B12 absorption
- Vegan and strict vegetarian diets — natural food sources of B12 are essentially limited to animal foods
- Some neurologic situations — when a prescriber is treating or preventing the nerve damage that B12 deficiency can cause
How do the forms and routes compare?
The table below describes what is and is not commercially available in the United States. It is a description of regulatory status and practical differences — not a ranking, and not a statement that any form is better for a particular person.
| Form | US status | Notes |
|---|---|---|
| Cyanocobalamin injection | FDA-approved | The standard, best-studied injectable B12 in the US; commercially available as 1,000 mcg/mL |
| Cyanocobalamin nasal spray (Nascobal) | FDA-approved | 500 mcg in one nostril once weekly; a non-injection option that is already on the market |
| Methylcobalamin injection | No FDA-approved drug product | Available only as a compounded preparation; used off-label |
| Hydroxocobalamin injection | No FDA-approved B12 product | Commonly used for B12 deficiency in Europe. In the US the only approved hydroxocobalamin is Cyanokit for cyanide poisoning, at a completely different (5 g) dose |
| Hydroxocobalamin nasal spray | Not FDA-approved | Compounded; the FDA-approved nasal B12 is cyanocobalamin |
| Custom strength | Compounded | Prepared as your prescriber orders |
Forms are listed for education only. High-quality evidence does not show that methylcobalamin or hydroxocobalamin is superior to FDA-approved cyanocobalamin. Your prescriber selects the form, dose, route, and schedule.
How is it used?
Use it exactly as your prescriber directs. Injectable B12 is given into a muscle (intramuscular) or under the skin (subcutaneous). Regimens vary, but a common pattern for a new diagnosis is frequent doses at first to refill your body's stores, then a much less frequent maintenance dose — the FDA label for cyanocobalamin injection describes 100 mcg daily for 6 or 7 days for pernicious anemia, then 100 mcg monthly for life (FDA cyanocobalamin injection label). Your own schedule and dose may look quite different; follow your label.
If you or a caregiver give the injections at home, use a new needle and syringe each time, clean the skin first, rotate injection sites, and dispose of sharps in a proper container. For the nasal spray, spray as directed; for the FDA-approved nasal cyanocobalamin, the label advises using it at least one hour before or after hot foods or liquids, since a runny nose can wash the dose away — the same practical point applies to a compounded nasal spray.
For most people, B12 is a long-term treatment. If the underlying cause has not gone away, stopping means the deficiency comes back. Do not stop or change the schedule on your own. A Bayview pharmacist is available for questions about your prescription.
How is deficiency diagnosed?
This is decided by your prescriber, not by the pharmacy. Testing usually starts with a serum vitamin B12 level, often alongside a complete blood count and a folate level. Serum B12 alone can be ambiguous in the borderline range, so prescribers frequently add methylmalonic acid (MMA) and homocysteine, which both rise in true B12 deficiency. That pairing also helps separate B12 deficiency from folate deficiency, where homocysteine rises but MMA stays normal (StatPearls, Vitamin B12 Deficiency).
Side effects & safety
Vitamin B12 is generally very safe. The National Institutes of Health notes that no upper intake level has been set for B12 because of its low potential for toxicity. Most people have no side effects at all.
What can happen:
- Injection site reactions — soreness, redness, or mild swelling where the shot was given
- Mild effects — diarrhea, headache, dizziness, or a sensation of swelling in the body
- Reddish discoloration — hydroxocobalamin is a deep red compound and can turn urine, and sometimes skin, reddish or pink. This is expected with hydroxocobalamin and is not harmful, but tell your prescriber if you notice it so it is not mistaken for blood in the urine.
- Hypersensitivity — rare, but anaphylaxis and death have been reported after injectable vitamin B12. Get emergency care for rash, hives, swelling of the face or throat, or trouble breathing.
Contact your prescriber about muscle weakness or cramping, leg pain or swelling, extreme thirst, palpitations, or any new or worsening numbness, tingling, or balance problems.
Who should not use it?
Vitamin B12 is not appropriate for everyone. Tell your prescriber your full health history, allergies, and all medications and supplements you take. In particular:
- Cobalt or vitamin B12 allergy. FDA labeling states that sensitivity to cobalt and/or vitamin B12 is a contraindication. Cobalt sits at the center of the B12 molecule.
- Leber's hereditary optic neuropathy. FDA labeling reports that patients with early Leber's disease treated with cyanocobalamin suffered severe and rapid optic atrophy, and cyanocobalamin products are not recommended in these patients.
- Severe megaloblastic anemia. Needs close monitoring during initial treatment, as above.
- Kidney disease, pregnancy, or breastfeeding. Discuss with your prescriber before starting.
Bayview Pharmacy does not provide consultations or determine whether this medication is appropriate for you. Only your prescriber can do that.
How should it be stored?
Follow your label exactly — it is the authority for your specific preparation. Most compounded B12 preparations from Bayview are refrigerated, and the higher-concentration hydroxocobalamin and methylcobalamin presentations always are. Vitamin B12 is also light-sensitive; FDA labeling for cyanocobalamin injection instructs in capitals to protect the product from light. Keep vials and syringes in their carton or an opaque bag, do not freeze unless your label says to, and keep them out of the reach of children.
Preservative-free single-dose vials and syringes are meant for one use — do not save leftovers from a single-dose container. Do not use a preparation past its beyond-use date, and do not use it if the solution looks cloudy or has particles in it. Dispose of unused medication and sharps as your pharmacist directs.
Why is this compounded?
Cyanocobalamin injection and nasal spray are commercially available, so compounding is used when the commercial products do not fit what the prescriber has ordered. The usual reasons are: the prescriber wants methylcobalamin or hydroxocobalamin, neither of which has an FDA-approved B12 product in the United States; the patient needs a preservative-free single-dose presentation; the order calls for a higher concentration than the commercial 1,000 mcg/mL vial so the injected volume stays small; or the patient is needle-averse and the prescriber wants a nasal spray in a form or strength that is not commercially made.
As a 503A compounding pharmacy, Bayview Pharmacy prepares each order in small batches as a sterile preparation under USP <797> standards using quality ingredients. Compounded preparations are not FDA-approved, and no claim is made that they work better than FDA-approved cyanocobalamin.
Clinical details for prescribers
Regulatory status. Vitamin B12 is not a controlled substance. Cyanocobalamin injection USP 1,000 mcg/mL is FDA-approved (e.g., ANDA 080737) and cyanocobalamin nasal spray (Nascobal, NDA 021642) is FDA-approved for B12 deficiency. There is no FDA-approved methylcobalamin drug product in the US, and no FDA-approved hydroxocobalamin product for B12 deficiency — hydroxocobalamin's only US approval is Cyanokit (5 g IV) for known or suspected cyanide poisoning. Methylcobalamin and hydroxocobalamin B12 replacement is therefore off-label and requires compounding. Compounded preparations are not FDA-approved.
Formulation & SIG. Preservative-free sterile injections: methylcobalamin 1 mg/mL (1 mL and 4 mL), 5 mg/mL (6 mL, refrigerated), 10 mg/mL (1 mL syringe); hydroxocobalamin 1 mg/mL (4 mL, 8 mL), 25 mg/mL (1 mL syringes or SDVs, refrigerated). Hydroxocobalamin 5 mg/mL nasal spray delivering 0.5 mg per 0.1 mL spray, 10 mL. Custom concentrations available. Typical SIG examples: inject 1 mL IM weekly × 4, then monthly; or 1 spray in one nostril weekly. Prepared under USP <797>.
Evidence & clinical points:
- NIH ODS: no evidence that absorption of B12 varies by supplement form; claims of methylcobalamin or hydroxocobalamin superiority over cyanocobalamin are not supported by high-quality comparative data
- B12 administration for fatigue or energy in non-deficient patients is not evidence-based; Bayview makes no such claims on the patient-facing page
- Diagnosis: serum B12 with reflex MMA (and homocysteine) in the 150–399 pg/mL borderline range; MMA elevated in B12 but not folate deficiency
- Folic acid >0.1 mg/day may induce hematologic remission while neurologic manifestations progress — do not treat empirically with folate alone
- Monitor potassium and platelets during intensive repletion of severe megaloblastic anemia (hypokalemia, sudden death reported)
- Contraindicated with cobalt/B12 hypersensitivity; not recommended in Leber's hereditary optic neuropathy (cyanocobalamin)
- Hydroxocobalamin produces chromaturia and cutaneous erythema; counsel patients so it is not mistaken for hematuria
- High-dose oral B12 (1,000–2,000 mcg daily) is a reasonable alternative to parenteral therapy in many patients, including some with pernicious anemia
Ordering: send a prescription to Bayview Pharmacy, or fax 401-284-4506. Background: NIH ODS Vitamin B12 fact sheet; Nascobal prescribing information.
This is a prescription compounded medication and is not FDA-approved. This information is educational and is not medical advice. Bayview Pharmacy does not provide consultations or determine whether a medication is appropriate; your prescriber makes that determination and sets the form, dose, and schedule.
