I take a B50 tablet daily and for probably a good nine months was taking 2000 mcg of extra B12.
Recently, my doctor asked me to take 5000 mcg of B12 for at least a period of time. He did not elaborate...but my thought was that at some point I would go back to the 2000 mcg. I have not had any side effects at all.
I have noticed that I feel better since taking the B50 and extra B12.