It’s a good question. I would suggest measure your B12 and if it’s mid range to high don’t take B12

While this is probably just you, or HCV related, it may require looking into.

Polycythemia (Rubra) Vera is the medical name for it if you want to Google.

Here’s what the Mayo Clinic has to say about it

http://www.mayoclinic.org/diseases-conditions/polycythemia-vera/basics/definition/con-20031013