Originally Posted by mrsD

B12 is really easy to tolerate. The only concern it has for high dose is for people with a rare blood condition called polycythemia vera.

If your doctor told you to do this, I'd do it. Just do it with methylcobalamin form. If you suspect a genetic problem, like the MTHFR mutations, then I'd add methylfolate to your supplements.
You can get tested to see if you have this mutation...it is turning out to be fairly common.