B12 that is in the blood has been absorbed, but there is no guarantee that it will be stored or used.

In almost all cases though, as the B12 result increases with treatment, and eventually gets very strong (around 1000 or more) it becomes very clear that stores are being filled, or have been filled. It is very unusual for someone to fail to build stores and use B12 well when taking 1000 - 2000 mcg cyanocobalamin per day, and it is even more unusual when taking methylcobalamin. Very rare.

Methylcobalamin has been proven safe in extremely large quantities, even regular doses in people who cannot remove it normally because of kidney disease.

rose