Can you overdose on vitamin b12?

Virtually nontoxic: At any dose. I do not believe that you will find very much written on the toxic effects of B12 although I have had a couple of patients who took something on the order of 10x what I had prescribed them was already in the 10,000IU range so they were taking about 100,000IU daily for several weeks and the patient developed diarrhea. When he stopped that resident, within several days diarrhea stopped

Some of the B12: liquid sub-lingual preparations have B6 as well. One that used to be advertised on a late night infomercial had a lot of B6 and some people were getting toxic from the B6. I recommend a sublingual liquid with 1.2 mg of B12 and 2 mg B6 per dose. Generally speaking you can't OD on B12 I recommend maintaining a blood level of >550.