"Normal" means nothing these days. The US considers very low levels as normal. Anything below 500 should be supplemented.

This is one of the most commonly overlooked results, and brings people to places like this in DROVES!

Get the number to make sure.

Drugs that deplete B12 or prevent it from being absorbed properly are:

acid lowering drugs -- both H2 antagonists like Zantac/Pepcid and proton pump inhibitors like Nexium/Prilosec and others in both families

Antibiotics (this would be long term use for chronic infections and Lyme)

Metformin (for PCOS, insulin resistance, or Type II diabetes)

Hormone therapy (birth control or HRT)
Colchicine
some antivirals for HIV

I searched you and found your question at another forum.
I'd like to say this....
While it is amazing what modern testing can do, it may not give
you answers you can use. You may have what was discussed there, or
not. What patients and doctors often lose sight of are the
things that are very obvious when looking for the obscure.
Do not assume that Mayo is the ultimate in medicine. Many people
go to Mayo and do not find the answers they expected.

What I do here is pull together information doctors may ignore.
The body is complex, and many things can be happening at once.
And often those get lost in the shuffle.

Oh, and BTW... I seriously doubt any of your doctors know about the new
melatonin information. Serum B12 testing is typical during a neuro screen. The sad part is that in the USA the "normal ranges" are vastly out of date and will confound your
treatment rather than help it.