can you od on b12 injections Vitamin B12: Effects, requirements and intake explained Ivy Grove Surgery : Self-administration

For patients without absorption disorders, high-dose oral supplements of 1,000 to 2,000 mcg daily have been shown to be comparably effective at correcting mild to moderate deficiency at lower cost and greater convenience.

Each has its own evidence base and safety boundary

Lower starting doses reveal individual sensitivity before committing to higher amounts

Gastrointestinal disturbances with B12 supplements typically relate to excipients such as sorbitol, mannitol, or lactose rather than the vitamin itself

The enzyme NNMT normally changes nicotinamide, a form of vitamin B3, by using methyl groups, which lowers nicotinamide adenine dinucleotide (NAD+) levels