I went from a low end of normal B-12 level to >1500 by taking a 500 mcg supplement daily. Stopping that for several months, the level dropped to 600. I am now taking the supplement once a week and the level seems to be stable.

I initially was given a 1000 mcg injection but that made me hyper. I could only tolerate the 500 mcg gummie. But too much of that was causing symptoms that could have been associated with colon cancer. Luckily the high level was discovered about the same time as the symptoms appeared.