I suspect that most of you already know this, but since there are a number of forum members in my age group, that are likely to need this vitamin supplement, I just want to say that a couple of doctors back, I was prescribed weekly shots of B12, however, the next doctor took me off them. When I complained, saying that they were about the only thing that I had been prescribed that actually made me feel better, he replied...of course, so does drugs. He wasn't talking about prescription drugs either.
Needless to say, I was very happy to hear that he had left the facility, and was given a third doctor. She didn't prescribe this for the first couple of years, but finally did on the last visit. However, what she prescribed was a low dose regimen, in lieu of monthly shots that I would have to go to the medical facility for. Not only were they low dose (500mcg) they were regular vitamin tablets that tasted terrible, and they had no effect on how I felt.
For this reason, I ordered some 2500mcg sub-lingual tablets from online, which just arrived today. I took one earlier, and a second one just shortly ago. Both times I felt an immediate improvement, which seems to last four hours.
Since they are not expensive, and are not toxic, nor can you overdose, I would recomend that everyone over 50 tries them. Perhaps even younger if you don't feel as good as you would like.