Hi i am 37 yr old woman, i was diagnosed with B12 deficiency 4 and half years ago. I have been having injections every 3 months since diagnosis, my question is if i have my injection during a menstrual period is it possible to loose the effectiveness of the injection due to the heavy bleed that i suffer. I have noticed a difference myself after having it during one period where i continued to stay very tired, bruising unnecessarily and generally low. I try very hard to have my injection after a period as believe having it right before or during the start of a period it just bleeds out. Please help is this the case my nurse did not seem to know and although there is no solution if this is case it can be avoided many thanks