There is no upper toxic level for B12.

You can look that up on any valid site.

On the first post of the B12 thread on
the PN forum is a link to a study published
by a doctor demonstrating 13 mcg are absorbed
from a 1000mcg oral dose. This is hardly
An alarming amount. Also on that table of
that paper is that a 1000mcg injection
results in only 150mcg measured in the
Serum.

You can copy that and give it to your
Doctor.

The only contraindication I have seen
is to not use B12 in patients with polycythemia
Vera which is a rare blood disease and
would show up in your testing so far. It
results in too many red blood cells.