Vitamin B12 can start to work quite quickly, especially through injections or high-dose oral supplements, with many people feeling an improvement in energy and reduction of symptoms within 24 to 72 hours. However, full benefits such as normalization of blood levels and neurological improvements may take longer—often between a few weeks up to 2-3 months depending on the severity of the deficiency, the form of B12 used, dosage, and individual health factors. Oral supplementation usually takes longer to show noticeable effects compared to injections, which have faster absorption directly into the bloodstream. Neurological symptoms caused by deficiency may take up to 3 months to improve significantly.
Summary of Timing
- Injections: Improvement often felt within 24-72 hours; blood levels may normalize in 1-2 months; neurological recovery up to 3 months
- High-dose oral/sublingual: Similar timeline to injections for initial improvement (around 24 hours), but full blood marker normalization may take up to 2 months
- Oral tablets: Typically take 2-4 weeks to start noticeable effects; full results may take 2-3 months
- Other forms (patches, nasal sprays): May take several days to weeks to show effects
Factors Affecting Response Time
- Severity of deficiency
- Form of B12 (methylcobalamin absorbs faster than cyanocobalamin)
- Dosage and frequency
- Individual absorption ability and health status (e.g., pernicious anemia slows absorption)
- Neurological symptom recovery requires longer durations
This means initial symptom relief can be quick, but complete recovery varies depending on individual circumstances.
