Some of the warnings on the Mayo site are for very rare circumstances. Yeah, if the doctors wait until you are so far gone that you have ANEMIA, then treatment for ANEMIA will spur the
bone marrow FAST and use potassium quickly since red cells have lots of potassium in them. Some very ANEMIC people can get temporary, signs of low potassium. But the general person does not have this problem. And never with ORAL...since so little is absorbed each dose. It is the massive INJECTION by DOCTORS which may be a problem. Some doctors give INJECTED cyano daily for a week or 10 days....and that is ALOT 1000mcg per dose.

The IV mention for hydroxcobalamin is for cyanide treatment, from smoke inhalation, or cyanide poisoning. B12 is typically not used IV except in some dramatic situations.

Polycythemia Vera is a very rare disease and will show up in regular screening blood work, and would be tagged hopefully by doctors before B12 injections.

The acne mentioned is also rare, few reports in the literature.
It is most likely from high INJECTED doses.

Studies of oral, show that about 13mcg only get absorbed from 1000mcg oral dose. At that intake, any symptoms of anything, are unlikely.

CYANOcobalamin is contraindicated in patients with the rare genetic disease called Leiber's optic neuritis, because these people cannot metabolize cyanide in any form.

B12 remains with no upper limit of toxicity for the vast majority of the population. The FDA has no upper limit posted for it.

One has to keep the clinical list from that Mayo site in perspective, therefore.