My husband was taking b12 injections twice a month for anemia. His b12 was checked by another doctor and it was 1999 so she backed it up to once a month. He immediately started feeling weak, extremely fatigued, slight vision problems and dizziness. He is 73. The doctor who initially put him on twice a month said for him to start doing that again. He said he had not heard of any problems from too much b12.