FYI, MrsD, I've finally started taking B12 at 1500 mcg first thing in the morning, and the first two days have gone just fine. No reactions like the D3, which I still have to reintroduce in another form/brand next week. I started low, as I do with all things, but perhaps I should up it to 3000 mcg. Not sure how much 1500 will do to improve things, but it seems to match with me. I think I tested as 515.