Reviewed by the Scan Dose Research Team and Clinical Advisory Board
Vitamin B12
LIMITED EVIDENCEVitaminLast updated April 5, 2026
SCAN DOSE SUMMARY
Vitamin B12 is an essential water-soluble vitamin critical for nerve function, DNA synthesis, and red blood cell production. Here's the honest truth: if you're not deficient, supplementing B12 does almost nothing. The evidence database is full of Grade D (no effect) ratings for cognition, depression, and fatigue in non-deficient people. But deficiency is common — especially in vegans, older adults, and people on metformin or acid-reducing drugs — and can cause irreversible nerve damage if untreated. Know your levels before supplementing.
Drugs that cause hypokalemia (diuretics, laxatives)Severe
Additive potassium lowering
Monitor potassium when starting IM B12 for anemia. Oral supplementation not a concern.
Supplements that cause hypokalemiaSevere
Additive potassium lowering
Monitor potassium.
SAFETY PROFILE
Side Effects
At typical oral doses: Very safe. Side effects uncommon.
At high oral doses (1,000 μg+): Mild GI symptoms (nausea, diarrhea, abdominal pain), headache
Acneiform eruptions: Vitamin B12 can cause acne-like lesions (comedones, papules, pustules) in atypical locations. Not responsive to standard acne treatments. Resolves when B12 is stopped.
Allergic reactions (rare): Itching, hives, tongue swelling, shortness of breath, hypotension. Uncommon but can range to life-threatening.
Hypokalemia (IM route only): When treating severe megaloblastic anemia, B12 injections can temporarily lower potassium as new red blood cells are rapidly produced.
Drug Interactions
Key insight: B12 has remarkably few drug interactions. However, many drugs deplete B12 — see below.
Nutrient Depletions (Drugs That Deplete B12)
Metformin — can reduce B12 levels. Mechanism involves calcium-dependent absorption. Supplementation effective. Calcium supplementation may also help.
Acid-lowering drugs (PPIs: omeprazole, lansoprazole; H2RAs: famotidine, ranitidine) — reduce B12 absorption from food by lowering stomach acid. Supplemental B12 (not food-bound) is not affected. Clinical significance debated.
Precautions
Pregnancy:Safe. Supplementation often recommended, especially for vegans/vegetarians. Deficiency can cause poor outcomes for the baby.
Breastfeeding:Safe. B12 is naturally in breast milk.
Myeloproliferative disorders (polycythemia vera):Avoid. B12 increases red blood cell production, which can worsen these rare blood cancers.
Leber disease (genetic optic neuropathy):Avoid. May worsen optic atrophy.
Impaired kidney function:Caution. Some cyanocobalamin supplements contain aluminum, which can accumulate and cause CNS toxicity in people with kidney impairment.
Diabetic nephropathy: High doses (1,000 μg) might worsen kidney function. More research needed.
WADA Status
Not Prohibited. Not on the 2026 WADA list.
WHO SHOULD BE CAREFUL
HOW SCAN DOSE SCORES THIS
Present in proper dose (2.4-1,000 μg):✅ Green flag — safe, essential vitamin. Important for at-risk groups (vegans, elderly, metformin users).
Underdosed (<1 μg):⚠️ Yellow flag — below RDA
Cyanocobalamin in kidney disease patient:⚠️ Yellow flag — aluminum accumulation risk
In a proprietary blend:Neutral — B12 is safe at a wide dose range, so blend risk is lower than most supplements
Marketed for energy/cognition in general population:⚠️ Yellow flag — evidence does NOT support benefits in non-deficient people. Misleading marketing.
CLINICAL REFERENCES
1.
Comprehensive review. B12 deficiency affects 6% of adults <60 and nearly 20% of those >60. Can cause irreversible neurological damage if untreated.
Green R et al. Vitamin B12 deficiency.. Nat Rev Dis Primers (2017). PMID: 34207137
2.
Vegans and vegetarians are at high risk of B12 deficiency. Supplementation is essential for these populations.
Rizzo G et al. Vitamin B12 among Vegetarians: Status, Assessment and Supplementation.. Nutrients (2016). PMID: 33847393
3.
Serum B12 levels <200 pg/mL indicate deficiency. Methylmalonic acid is the most sensitive confirmatory test.
Langan RC et al. Update on Vitamin B12 Deficiency.. Am Fam Physician (2017). PMID: 29248320
4.
Long-term metformin use significantly associated with B12 deficiency. Periodic monitoring recommended.
Aroda VR et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study.. J Clin Endocrinol Metab (2016). PMID: 28660890
5.
B12 supplementation alone does not improve cognition or mood in non-deficient populations.
Ford TC et al. The Effect of Vitamin B Supplementation on Mood, Cognition, and Well-being in Healthy Adults.. Nutr Neurosci (2018). PMID: 34521255